Blog
Practical guides for everyday conversions, and honest explainers on how online tools handle your data.
Posts are contributed and editorially reviewed — corrections and suggestions welcome via the contact page.
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Pets & Animals · explainer
The 1 Inch Per Gallon Rule Is Wrong — What Actually Limits Fish Stocking
The inch-per-gallon rule fails because waste scales with body mass, not length — one 10-inch fish is nowhere near ten 1-inch fish. Here's what really sets your limit: adult size, bioload, surface area, filtration and territory.
2026-07-18
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Music & Audio · explainer
BPM to Delay Time: The 60,000 Rule Every Producer Should Know
Quarter-note delay in milliseconds is 60,000 ÷ BPM — 500 ms at 120 BPM. Here's the full subdivision table, how dotted and triplet delays work, and why the dotted eighth is the most useful delay setting in pop production.
2026-07-18
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Photography · explainer
Crop Factor Explained: Your 50mm Doesn't Become a 75mm (and f/1.8 Is Still f/1.8)
Crop factor is the ratio between your sensor and 35mm film. It changes framing, not the lens. Here's why a 50mm on APS-C frames like a 75mm, why exposure never changes, and the one place the aperture multiplication is real.
2026-07-18
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Weather & Atmosphere · explainer
Dew Point vs Relative Humidity: Why 100% Humidity Can Feel Fine and 50% Can Feel Awful
Relative humidity depends on temperature, so it tells you almost nothing about comfort. Dew point measures the actual moisture in the air. Here's the comfort scale, why sweat is the mechanism, and why 100% RH at 30°F feels dry.
2026-07-18
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Travel & Trips · explainer
How Long Does Jet Lag Last? Why Flying East Is Worse — and How to Cut Recovery in Half
Jet lag lasts roughly one day per time zone flying west, but about 1.5 days per zone flying east. Here's the circadian reason east is harder, and how correctly timed light exposure compresses recovery to 2–3 zones a day.
2026-07-18
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Travel & Trips · explainer
How Much Layover Time Do You Need? Minimum Connection Times vs. What's Actually Safe
Airlines allow domestic connections as short as 30 minutes, but the realistic minimum is 60–90 minutes domestic and 2–3 hours international. Here's what minimum connection time really means, why it's optimistic, and the one factor that matters more than the clock.
2026-07-18
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Homebrewing · explainer
IBU Explained: Why Your 60 IBU Beer Doesn't Taste Twice as Bitter as a 30
IBU measures dissolved iso-alpha acids in mg/L, but perceived bitterness depends on malt sweetness too. Here's how the Tinseth formula works, why boil time and wort gravity change hop utilisation, and why BU:GU predicts balance better than IBU alone.
2026-07-18
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Astronomy & Space · explainer
Moon Phases Explained: Why There Are 8, Why They Take 29.5 Days, and Why There's No Dark Side
The Moon's phases come from the changing angle between the Sun, Earth and Moon — not from Earth's shadow. Here's the 8-phase cycle, why the synodic month is 29.5 days rather than 27.3, and why the far side isn't dark.
2026-07-18
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Home & DIY · explainer
How Deep Should a Paver Base Be? Gravel, Sand and the Mistakes That Sink Patios
A paver patio needs 4–6 inches of compacted gravel plus 1 inch of bedding sand; a driveway needs 8–12. Here's why compaction happens in thin lifts, why the sand layer must stay thin, and the two omissions that ruin most DIY paver jobs.
2026-07-18
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Home & DIY · explainer
Rebar in a Concrete Slab: Spacing, Cover and Lap Splices Explained
Residential slabs typically use #4 bar at 12–18 inches on centre with 3 inches of cover. Here's how to work out bar counts, why cover matters more than people think, and where the '40 bar diameters' lap rule differs from what the code actually requires.
2026-07-18
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Astronomy & Space · explainer
Telescope Magnification: Why the '600x' on the Box Is a Lie
Magnification is telescope focal length ÷ eyepiece focal length — but the useful limit is about 50× per inch of aperture. Here's why aperture beats magnification, what exit pupil means, and why planetary observers deliberately use less power.
2026-07-18
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Automotive · explainer
Why Your Tire Pressure Light Comes On in Winter (1 PSI per 10°F, Explained)
Tires lose roughly 1 PSI for every 10°F the temperature drops — so an overnight cold snap can trigger your TPMS light with no leak at all. Here's the physics, when 'cold' pressure actually means cold, and why you shouldn't overinflate to compensate.
2026-07-18
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Home & DIY · explainer
Roof Pitch Explained: 4/12 in Degrees, Walkability, and Minimum Slopes by Material
Roof pitch is rise per 12 inches of run — a 4/12 roof rises 4 inches every 12 across, which is 18.4°. Here's the pitch-to-degrees chart, which roofs are safe to walk, and the minimum slope asphalt shingles and tile actually require.
2026-07-17
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Productivity · explainer
What Is a Swimlane Diagram? Mapping Who Does What (and Where Work Stalls)
A swimlane diagram is a flowchart split into lanes, one per role or team, so every hand-off between them becomes a visible arrow. Here's when to use one, how many lanes to draw, lanes vs pools in BPMN, and how to read the hand-offs where delays hide.
2026-07-17
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Charts & Design · explainer
Which Chart Type Should You Use? A Decision Guide (Bar, Line, Pie, Funnel, Radar, Waterfall)
Bar charts compare categories, line charts show change over time, pie charts show parts of a whole. Here's a decision framework for picking the right chart — plus when funnel, radar and waterfall charts beat all three, and the mistakes that make charts lie.
2026-07-17
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Calculators · explainer
How to Calculate Square Footage of a Room (Including L-Shapes and Odd Angles)
Square footage is length × width. For a 12 × 10 ft room that's 120 sq ft. Here's how to handle L-shaped rooms, circles and triangles, how much waste to add for flooring, and how to convert to square metres.
2026-07-14
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Home & DIY · explainer
What Is a Cord of Wood? Full Cord vs Face Cord (and How Not to Get Shorted)
A cord of firewood is a stack measuring 4 ft × 4 ft × 8 ft — exactly 128 cubic feet. A 'face cord' is only one log deep, so it's often just a third of that. Here's how to measure a delivery, spot a short cord, and convert between the two.
2026-07-14
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Pets & Animals · explainer
How Much Chocolate Is Toxic to Dogs? (Type, Weight & Dose Explained)
Chocolate poisons dogs through theobromine, and the danger depends on the type of chocolate and your dog's weight. Here's how the dose works, the risk thresholds vets use, and exactly what to do if your dog ate chocolate.
2026-07-13
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Network & IT · explainer
Mbps vs MB/s: Why Your Download Is 8× Slower Than Your Internet Plan
Your 100 Mbps plan downloads files at about 12.5 MB/s — not 100. The reason is bits versus bytes: there are 8 bits in a byte, so you divide Mbps by 8 to get MB/s. Here's the full explanation, a conversion table, and how to estimate download times.
2026-07-13
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3D Printing · explainer
Why a Bigger 3D Print Uses So Much More Filament: The Cube Rule
Scaling a model to 200% doesn't use twice the filament — it uses eight times. That surprise trips up almost everyone new to 3D printing. Here's the simple cube rule behind it, why print time balloons the same way, and how to plan a resize.
2026-07-12
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Photography · explainer
How to Blur the Background: The 4 Keys to Depth of Field
That creamy blurred background comes from a shallow depth of field — and four things control it: aperture, focal length, subject distance and sensor size. How each one works, and the exact recipe for a blurry background or front-to-back sharpness.
2026-07-12
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Pets & Animals · explainer
How Old Is My Dog in Human Years? The 7-Year Myth, Debunked
Multiplying a dog's age by 7 is a myth — dogs mature fast then age slowly. A 1-year-old dog is roughly a 15-year-old human, not 7. The better methods: the 2020 epigenetic formula (16 × ln(age) + 31) and the size-based chart, explained with a worked example.
2026-07-12
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Physics · explainer
Elastic vs Inelastic Collisions: What's Conserved (and Why)
Momentum is conserved in every collision — but kinetic energy is only conserved in an elastic one. Here's the difference, the formulas for the final velocities, where the 'lost' energy goes, and the coefficient of restitution that ties it all together.
2026-07-12
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Weather & Atmosphere · explainer
Why 'Feels Like' Isn't the Temperature: Heat Index, Wind Chill and Wet-Bulb
The thermometer only tells half the story. In humid heat, sweat can't evaporate — the heat index. In cold wind, heat is stripped away — the wind chill. And the wet-bulb temperature sets the hard limit on how much the body can cool at all. What each means and when it matters.
2026-07-12
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Finance · explainer
Financial Ratios Explained: The 6 Families and How to Read Them
A single ratio is just a number — its meaning comes from what you compare it to. Here's a plain-English tour of the six families of financial ratios (liquidity, leverage, coverage, profitability, efficiency, valuation), the formulas, the healthy benchmarks, and which ratios only make sense against industry peers.
2026-07-12
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Astronomy & Space · explainer
Golden Hour and Blue Hour: The Sun Angles That Make the Best Light
Golden hour isn't a clock time — it's a sun angle. Here's exactly which elevations define golden hour, blue hour and the three twilights, why the windows are longer some places than others, and how to find them for any date and location.
2026-07-12
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Travel & Trips · explainer
Why Flight Paths Curve on the Map: Great-Circle Distance
A flight from New York to London arcs north on a flat map instead of running straight across — not to avoid anything, but because the shortest path over a round Earth is a great circle. Here's what that means, why the map lies, and how the distance is actually calculated.
2026-07-12
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Solar & Energy · explainer
How Many Solar Panels Do I Need? A Simple Way to Size a System
The answer isn't a fixed number — it depends on how much energy you use and how much sun you get. Here's the simple three-step method to size a solar array, with a worked example and the margin to add for real-world conditions.
2026-07-12
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Finance · explainer
How Much House Can You Afford? The 28/36 Rule Explained
Lenders don't ask what you want to spend — they check two ratios against your income. Here's how the 28/36 rule works, how to turn it into a real home-price ceiling, and why the number it gives is a limit, not a target.
2026-07-12
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Homebrewing · explainer
How to Calculate ABV: Original Gravity, Final Gravity and Alcohol
Your beer's alcohol content is hiding in two hydrometer readings. Here's what original and final gravity mean, the simple formula that turns them into ABV, when to reach for the more accurate one, and the mistakes that throw the number off.
2026-07-12
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Electronics & Circuits · explainer
How to Read SMD Resistor Codes (103, 4700, 01C and R47)
Surface-mount resistors print a tiny number instead of color bands — and the rules aren't obvious. Here's how to decode 3-digit, 4-digit, EIA-96 and R-notation markings, why 470 means 47 ohms, and how to read the zero-ohm jumper.
2026-07-12
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Astronomy & Space · explainer
Why You Always See Space in the Past: Light Travel Time Explained
Light is fast but not instant, and space is vast — so every time you look up, you see the past. The Sun as it was 8 minutes ago, the nearest star 4 years ago, distant galaxies millions of years back. How light travel time works, and what a light-year really is.
2026-07-12
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Music & Audio · explainer
Why Every Octave Doubles: The Math Behind Musical Notes
Every musical note is a frequency, and the system is beautifully simple: an octave doubles the frequency, and twelve equal semitone steps divide it, each multiplying by the twelfth root of 2. Why A = 440 Hz, what cents are, and why a piano's fifths aren't quite pure.
2026-07-12
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PDF Tools · explainer
How to Convert a PDF to JPG Without Uploading It
Most 'PDF to JPG' sites upload your document to their servers to do the conversion — a problem when it's a contract, a bank statement or an ID. Here's how to convert PDF pages to images entirely in your browser, and how to choose JPG vs PNG and the right resolution.
2026-07-12
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Privacy & Security · explainer
How to Redact Personal Data Before Pasting Text Into AI
Pasting an error log, email or spreadsheet row into ChatGPT is convenient — and an easy way to leak customer data. Here's why it matters, what counts as PII, and how to strip it out locally in seconds before you hit send.
2026-07-12
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Electronics & Circuits · explainer
How to Read a Resistor Color Code (Bands to Ohms)
A resistor's colored bands are a compact code: the first two are digits, the next is a ×10ⁿ multiplier, and the last is tolerance. Learn the color values, how to tell which end to start from, and how 4, 5 and 6-band resistors differ — with a worked example.
2026-07-12
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Biology & Lab · explainer
How to Predict Restriction Digest Fragment Sizes
A restriction digest cuts DNA into fragments — and you can predict their sizes from the sequence before you run the gel. Here's how cut positions become fragment sizes, why linear and circular DNA differ, and what the prediction can't tell you.
2026-07-12
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Gardening & Plants · explainer
When to Start Seeds: Timing Your Whole Garden to the Last Frost
One date runs the whole vegetable garden: your average last spring frost. Start tomatoes indoors ~7 weeks before it, sow peas 5 weeks before, plant beans after it. How frost-relative timing works, a crop-by-crop guide, and how to turn it into real dates.
2026-07-12
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Mathematics · explainer
How to Solve a Triangle (Law of Sines & Law of Cosines)
Given a few sides and angles of a triangle, you can find all the rest — if you know which rule to use. Here's how to pick between the law of sines and the law of cosines for each case (SSS, SAS, ASA, AAS), and why SSA is the tricky one.
2026-07-12
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Statistics · explainer
The t-Test Explained: One-Sample, Two-Sample and Paired
A t-test answers one question: is a difference in means real, or could it be chance? Here's how the three types work, how to pick between Welch and pooled, what the p-value actually tells you, and the mistake almost everyone makes reading a non-significant result.
2026-07-12
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Weather & Atmosphere · explainer
What Is VPD? Vapor Pressure Deficit Explained (with Target Ranges)
VPD — vapor pressure deficit — is the single number serious growers tune instead of humidity, because it accounts for temperature. Here's what it means, how it's calculated, and the target VPD ranges for each growth stage.
2026-07-12
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Chemistry & Lab · explainer
How to Find the pH of a Weak Acid (the ICE-Table Method)
A weak acid at 0.1 M isn't pH 1 — it's closer to 3, because it barely ionizes. Here's why −log of the concentration fails, how to set up the ICE table, and how to solve for pH exactly instead of guessing that 'x is small'.
2026-07-12
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Chemistry & Lab · explainer
How to Balance Chemical Equations: The Algebra Method (Step by Step)
Balancing a chemical equation is exact algebra: one unknown per species, one equation per element, solved for the smallest whole numbers. The step-by-step method, worked examples, and why it's the reliable way to balance redox reactions that chatbots get wrong.
2026-07-11
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Chemistry & Lab · explainer
Colligative Properties: Why Salt Melts Ice and Antifreeze Works
Colligative properties depend on the number of dissolved particles, not their identity. Freezing-point depression (ΔTf = i·Kf·m) and boiling-point elevation (ΔTb = i·Kb·m), the van't Hoff factor, and why 1 molal NaCl drops water's freezing point by 3.72 °C.
2026-07-11
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Color Tools · explainer
Accessible Color: Contrast Ratios and Color Blindness, Explained
Accessible color rests on two things: enough contrast (WCAG AA needs 4.5:1 for text, 3:1 for large text) and not relying on color alone (~1 in 12 men are color-blind). How the ratios work, what deuteranopia/protanopia/tritanopia change, and how to fix a failing color.
2026-07-11
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Color Tools · explainer
Extracting Colors from an Image: Pickers, Palettes and Naming
Three ways to pull colors out of an image, all on-device: pick a pixel for its exact HEX/RGB/HSL (or use the EyeDropper API), extract a dominant palette with median-cut, and find the nearest CSS color name by CIEDE2000. How each works and why nothing is uploaded.
2026-07-11
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Finance · explainer
Debt Snowball vs Avalanche: Which Pays Off Debt Faster?
The avalanche method (highest interest rate first) always costs the least interest; the snowball method (smallest balance first) gives faster psychological wins. Both keep the same monthly budget — only the target order changes. How each works, a worked example, and how to decide.
2026-07-11
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Home & DIY · explainer
How Much Do I Need? Estimating Paint, Tile, Concrete and Mulch
Every home-project estimate is either an area job (paint, tiles) or a volume job (concrete, mulch). Area = length × width; volume = area × depth. The formulas, sensible coverage and waste allowances, and how to turn them into cans, tiles, bags and rolls.
2026-07-11
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Cooking & Kitchen · explainer
Grams to Cups: Why a Cup of Flour Isn't a Cup of Sugar
A cup measures volume, but grams measure weight — so one cup weighs a different number of grams for every ingredient: about 120 g of flour, 198 g of sugar, 336 g of honey. Why there's no single grams-per-cup number, and why weighing beats scooping.
2026-07-11
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Text Tools · explainer
Homoglyph Attacks: How Lookalike Characters Spoof Domains and Brands
“pаypal.com” with a Cyrillic а looks identical to the real thing but is a different address. How homoglyph (IDN homograph) attacks use confusable Unicode characters for phishing, why mixed scripts are the giveaway, and how to detect them.
2026-07-11
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Text Tools · explainer
Invisible Characters in Text: Zero-Width Spaces, Hidden Watermarks, and How to Remove Them
A zero-width space (U+200B) is invisible on screen but real in the bytes — it breaks search, code and CSV parsing, and tag characters (U+E0000–E007F) can invisibly watermark AI text. What the hidden characters are, why they matter, and how to detect and strip them.
2026-07-11
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Chemistry & Lab · explainer
Oxidation Numbers: The Rules and How to Assign Them
Oxidation numbers follow a short priority list of rules — group 1 is +1, oxygen is −2, hydrogen is +1 — and the last unknown falls out by making everything sum to the overall charge. The rules in order, worked examples like KMnO₄ → Mn +7, and the exceptions.
2026-07-11
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Color Tools · explainer
OKLCH: The Modern CSS Color Format (and How to Convert from HEX)
OKLCH is a perceptually uniform color format — oklch(L% C H) — now supported in ~95% of browsers and Tailwind CSS 4's default. Why it beats HEX and HSL for building shade ramps, how to convert HEX to OKLCH, and why you still keep a HEX fallback.
2026-07-11
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Text Tools · explainer
Readability Scores Explained: Flesch Reading Ease, Grade Level, and How to Improve Them
Flesch Reading Ease scores text 0–100 (higher is easier); Flesch-Kincaid, Gunning Fog, SMOG, Coleman-Liau and ARI give a US grade level. What the scores mean, the formulas behind them, what to aim for, and how shorter sentences and simpler words move the numbers.
2026-07-11
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Chemistry & Lab · explainer
How to Read the Periodic Table: Groups, Periods, Blocks and Trends
The periodic table is organised so position predicts behaviour: columns (groups) share chemistry, rows (periods) count electron shells, and blocks show which orbital fills. How to read it, plus the key trends — electronegativity, atomic radius and reactivity.
2026-07-11
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Home & DIY · explainer
How Many Shingles Do I Need? Roofing Squares and Pitch Explained
A roof is bigger than its footprint because it slopes. Multiply the footprint by the slope factor √(1 + (rise/run)²), convert to roofing squares (1 square = 100 sq ft), then to shingle bundles (usually 3 per square). Worked examples and how much to add for waste.
2026-07-11
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Fitness & Exercise · explainer
The Runner's Math: Pace, Race Times and Heart-Rate Zones Explained
Three formulas cover almost all of running math: pace = time ÷ distance, Riegel's race predictor (t2 = t1 × (d2/d1)^1.06), and heart-rate zones from your max HR. What each means, worked examples, and how to use them to train and race smarter.
2026-07-11
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Statistics · explainer
How Many People Do You Need to Survey? Sample Size Explained
The sample size for a proportion is n = z²·p(1−p) / E². At 95% confidence with a ±5% margin you need 385 responses — whether your population is 20,000 or 20 million. Why p = 0.5 is the safe choice, why halving the margin quadruples n, and when population size matters.
2026-07-11
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Physics · explainer
Series vs Parallel: Resistors and Capacitors (and Why They're Opposite)
Resistors in series add; in parallel their reciprocals add (total below the smallest). Capacitors do the exact reverse. The rules, the reason, a memory aid, and worked examples — so you never mix them up again.
2026-07-11
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Physics · explainer
The SUVAT Equations: Solve Any Constant-Acceleration Problem
The five SUVAT kinematic equations link displacement, initial and final velocity, acceleration and time. Know any three and you can find the other two. How to pick the right equation, worked examples, and why they only work for constant acceleration.
2026-07-11
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Chemistry & Lab · explainer
The Mole Explained: Converting Grams, Moles and Molecules
The mole is the hub of chemistry calculations: moles = mass ÷ molar mass, and particles = moles × Avogadro's number (6.022×10²³). How to convert between grams, moles and molecules, why one mole equals the molar mass in grams, and how it drives stoichiometry.
2026-07-11
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Automotive · explainer
How to Read a Tire Size: 225/45R17 Decoded
A tire size like 225/45R17 packs four facts into one code: section width in millimetres (225), aspect ratio as a percentage (45), radial construction (R), and rim diameter in inches (17). What each part means, how to find the real overall diameter, and why part is metric and part is inches.
2026-07-11
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Generators · explainer
WiFi QR Codes: How They Work, the WIFI: Format, and How to Make One Safely
A WiFi QR code encodes the string WIFI:T:WPA;S:network;P:password;; — scan it and a phone joins the network with no typing. How the format works, why special characters must be escaped, and why encoding it directly (not via a tracking redirect) matters.
2026-07-11
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Statistics · explainer
Z-Score to P-Value: How to Read the Normal Distribution
A p-value is the tail area of the normal curve beyond your z-score. z = 1.96 gives a two-tailed p of 0.05; z = 1.645 a one-tailed p of 0.05. How the conversion works, one- versus two-tailed, and why a table is coarser than the exact erf calculation.
2026-07-11
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Color Tools · explainer
Brand Colors: The Exact Hex Codes of Famous Brands — and How to Use Them Legally
Netflix red is #e50914, Spotify green #1db954, Tiffany blue #0abab5. Where to find the exact hex codes of 1,100+ brands, why colors themselves aren't owned, and where using a brand's palette crosses from normal design practice into trademark trouble.
2026-07-10
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Network & IT · explainer
chmod 755 Explained: Unix File Permissions Without the Guesswork
What chmod 755 actually means, how the numbers work (read=4, write=2, execute=1), the difference between 644 and 755, when to use 600, and why chmod 777 is almost always the wrong fix. With the setuid/setgid/sticky bits explained.
2026-07-10
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Network & IT · explainer
Cron Syntax Explained: The Five Fields, the Shortcuts, and the OR-Rule Trap
How cron expressions work: the five fields (minute, hour, day-of-month, month, day-of-week), the special characters (* , - /), what */15 means, and the day-of-month/day-of-week OR-rule that makes jobs run more often than expected.
2026-07-10
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Biology & Lab · explainer
C1V1 = C2V2: How to Calculate Any Dilution (with Serial Dilutions)
The dilution equation C1V1 = C2V2 conserves solute, so the stock volume you need is V1 = C2V2/C1. To make 100 mL of 1× from a 10× stock: 10 mL stock + 90 mL diluent. How to solve for any unknown, plan a serial dilution, and why units cancel.
2026-07-10
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Biology & Lab · explainer
Hardy–Weinberg Equilibrium: Allele Frequencies, p²+2pq+q², and the χ² Test
Hardy–Weinberg predicts genotype frequencies from allele frequencies: p²+2pq+q²=1. Find p and q from genotype counts (p = (2·AA+Aa)/2N), compute expected counts, and test for equilibrium with a chi-square goodness-of-fit — with a worked example.
2026-07-10
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Calculators · explainer
Markup vs Margin: Same Profit, Two Very Different Percentages
Buy for $60, sell for $100: that's a 66.7% markup but a 40% margin — the same $40 profit measured against cost vs against price. Why markup is always bigger, how to convert between them, and the pricing mistake that quietly eats your profit.
2026-07-10
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Calculators · explainer
Why Your First Mortgage Payment Is Almost All Interest
On a $300k loan at 6%, payment #1 is $1,500 interest and just $299 principal — because interest is charged on the balance you still owe, and early on you owe nearly everything. How amortization works, why total interest can exceed the loan, and how extra principal shortens it.
2026-07-10
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Photo Size Maker · reference
Passport Photo Size by Country: The Complete Guide (2026)
Most countries use the ICAO 35×45 mm photo, the US uses 2×2 inches, and there are real outliers — Spain 26×32, Canada 50×70, China 33×48, Kenya 55×55. The size, background colour and file rules for passport and visa photos worldwide, with a country-by-country table.
2026-07-10
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Biology & Lab · explainer
Punnett Squares: Monohybrid, Dihybrid, and Where the 9:3:3:1 Comes From
A monohybrid Aa × Aa cross gives 1:2:1 genotypes and a 3:1 phenotype ratio; a dihybrid AaBb × AaBb gives 9:3:3:1. How to fill the grid, read the ratios, and why larger crosses are so easy to get wrong by hand.
2026-07-10
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Biology & Lab · explainer
Reverse Complement of DNA: The Rule, the Steps, and Why Direction Matters
The reverse complement of ATGC is GCAT — complement each base (A↔T, G↔C), then reverse to read 5′→3′. Why it's not the same as the complement, how translation and transcription differ, and why you shouldn't paste sequences into a chatbot.
2026-07-10
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Mathematics · explainer
Significant Figures: The Rules, the Ambiguous Cases, and How to Round Correctly
How many significant figures does 0.004560 have? Why is 1200 ambiguous? The four sig-fig rules explained digit by digit, how to round to N significant figures (including the 9.99 carry case), and why the rules exist at all.
2026-07-10
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Calculators · explainer
BMR vs TDEE: How Many Calories You Actually Need (and Why)
Your BMR is what you burn at rest; your TDEE is BMR times an activity factor — the real number that decides whether you lose, hold or gain. The Mifflin–St Jeor formula, the five activity multipliers, and how to set a deficit, worked through step by step.
2026-07-10
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Mathematics · explainer
0.1 + 0.2 ≠ 0.3: Why Most Calculators Quietly Round — and What Exact Arithmetic Looks Like
Every ordinary calculator computes in floating point, which silently rounds past ~15 digits, turns 1/3 + 2/3 into 0.9999999999999999, and overflows at 171!. How exact rational and big-integer arithmetic avoids all of it — and when the difference actually matters.
2026-07-09
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PDF Tools · explainer
PDF Accessibility After the EAA: What a Screen Reader Actually Needs From Your PDF
The European Accessibility Act has applied since June 2025, and PDFs inside e-commerce, banking and e-book services are in scope. What makes a PDF readable to assistive technology — tags, language, title, text layer, alt text — which checks a machine can run, and how to triage a document in your browser.
2026-07-08
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PDF Tools · explainer
Why PDF Redactions Keep Failing — and How to Redact (and Verify) for Real
From the Epstein files to routine court filings, 'redacted' PDFs keep leaking their contents because black boxes hide text instead of removing it. How redaction actually fails, how to do it irreversibly by flattening, and the ten-second verification everyone skips.
2026-07-08
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File Converters · explainer
France's 2026 E-Invoicing Mandate: How to Open a Factur-X Invoice Without Accounting Software
From 1 September 2026, every French company must be able to receive electronic invoices — most arriving as Factur-X hybrid PDFs. What the mandate requires, how a Factur-X file is structured, what the five profiles mean, and how to read one privately in your browser.
2026-07-07
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Network & IT · explainer
IPv6 Crossed 50%: A Practical Subnetting Guide for the Dual-Stack Era
IPv6 now carries the majority of traffic to major services. What that means in practice: how IPv6 addresses are structured, why every LAN is a /64, how /48 and /56 allocations work, and the habits to unlearn from IPv4 subnetting.
2026-07-07
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File Converters · explainer
KSeF in 2026/2027: How to Open and Read an FA(3) Invoice XML — No Software, Nothing Uploaded
Poland's KSeF makes the XML the legally binding invoice — mandatory for all VAT businesses since April 2026, with penalties from January 2027. What the FA(3) structure contains, how the clearance model works, and how to read or pre-check an FA(3) file in your browser.
2026-07-07
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Developer Tools · explainer
LLM Tokens Explained: What Your Prompts Actually Cost — and Why Claude & Gemini Counts Are Estimates
API bills are denominated in tokens, not words. How tokenization works, the cost formula, verified July 2026 pricing for GPT-5.x, Claude and Gemini, why output tokens dominate the bill, and why only OpenAI counts can be exact in a browser.
2026-07-07
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Calendars · explainer
The 4-5-4 Retail Calendar Explained: Why Retailers Don't Use Normal Months
The NRF 4-5-4 calendar splits the retail year into 13-week quarters of 4-5-4 week months so sales compare like-for-like. How it works, when the retail year starts, why some years have 53 weeks, and how to find any date's retail week.
2026-07-06
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Calendars · explainer
Hijri, Hebrew, Persian and Julian: How the World's Calendars Actually Work
Why is the Islamic year 1447 while the Gregorian is 2026? A guide to the world's major calendar systems — lunar, solar and lunisolar — how they differ, and how to convert any date between them in your browser.
2026-07-06
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Codes & Ciphers · explainer
Morse, NATO, Binary and Classic Ciphers: Codes You Can Actually Read
Morse code, the NATO phonetic alphabet and binary are encodings anyone can reverse; the Caesar, ROT13 and Vigenère ciphers scramble text with a key. What each one is, how they differ from real encryption, and when to use them.
2026-07-06
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File Converters · explainer
Received an Invoice as an XML File? XRechnung and ZUGFeRD Explained
Germany's B2B e-invoicing mandate means invoices now arrive as XRechnung XML or ZUGFeRD hybrid PDFs. What the formats are, why you're getting them, the 2025–2028 timeline, and how to actually read one.
2026-07-06
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Image Tools · explainer
Why iPhone Photos Won't Open on Windows — HEIC Explained (and How to Convert It)
iPhones save photos as HEIC — half the size of JPEG, but unreadable on Windows, Android and the web. What HEIC is, why it breaks things, how to convert it privately, and how to make your iPhone shoot JPEG instead.
2026-07-06
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Calendars · explainer
BS to AD (and Back): How the Nepali Bikram Sambat Calendar Works
Nepal runs on Bikram Sambat, about 56 years 8 months ahead of the Gregorian calendar — so 2024 AD is 2081 BS. Why BS months have no fixed length, how conversion actually works, and how to convert any date both ways.
2026-07-06
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PDF Tools · how-to
How to Password-Protect a PDF (or Remove a Password) Without Uploading It
PDF encryption uses AES — but 'free online' unlock tools ask you to upload the document and its password together, the two things you should never send anywhere. How PDF passwords work and how to add or remove them locally.
2026-07-06
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Productivity · explainer
The Pomodoro Technique: Why 25-Minute Sprints Beat Marathon Focus
The Pomodoro Technique breaks work into 25-minute focus sprints with short breaks. Why the timer works, how to run it properly, the mistakes that break it, and how to tune the intervals to your attention span.
2026-07-06
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Productivity · explainer
Privacy-First Productivity: Plan, Focus and Track Without the Cloud
Notion, Trello and Todoist keep your tasks on their servers. A different approach: single-purpose productivity tools that run in your browser, save to your device, and never upload a thing — Pomodoro, Eisenhower matrix, habit tracker and more.
2026-07-06
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Text Tools · explainer
Character Limits Cheat Sheet: X/Twitter, SMS, Google, Instagram and More
X allows 280 characters (URLs count as 23), one SMS is 160, Google shows ~60 of a title and ~158 of a meta description. The full limits table, the emoji trap, and how to count reliably.
2026-07-05
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Developer Tools · explainer
Base64 Is Not Encryption: What It Actually Does (and When to Use It)
Base64 turns any bytes into 64 safe text characters — 3 bytes become 4 characters, 33% bigger, instantly reversible by anyone. What it's for, how the encoding works, the URL-safe variant, and why JWTs are readable by design.
2026-07-05
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Text Tools · how-to
How to Clean Up Any Messy List: Dedupe, Sort and Fix Broken Text in 4 Steps
The repeatable pipeline for messy pasted data: fix broken line breaks, remove duplicates (with the invisible-spaces trap), natural-sort, and pattern-fix with find & replace — each step one click.
2026-07-05
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Size Converters · explainer
Women's Clothing Size Conversion: US, UK, EU, IT Charts — and Why Vanity Sizing Broke Them
A US 8 is a UK 12, EU 38, FR 40, IT 44 and JP 13. Get the full conversion chart, the fixed offsets behind it, and why a 1975 size 12 became today's size 6.
2026-07-05
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Color Tools · explainer
HEX, RGB, HSL and CMYK: CSS Color Formats Explained (With Conversion Math)
#1d87f1 = rgb(29, 135, 241) = hsl(210, 88%, 53%) — the same color in three dialects. How each format works, when to use which, the manual conversion math, and why CMYK never quite matches.
2026-07-05
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File Converters · how-to
CSV to JSON Without the Traps: Quotes, Commas, Semicolons and Typed Values
Converting CSV to JSON fails in predictable ways: commas inside quoted fields, semicolon Excel exports, and numbers arriving as strings. How the conversion actually works, both directions, with fixes for every trap.
2026-07-05
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Privacy & Security · explainer
What Your Photos Reveal: EXIF, GPS Location and How to Strip Them
Phone photos embed EXIF metadata — camera, timestamps and, with location on, GPS coordinates accurate to a few meters. What's in the file, which sharing channels leak it, and how to remove it in your browser.
2026-07-05
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Size Converters · explainer
Hat Sizes Decoded: Why 7⅛ Means Your Head's Diameter (Charts + Measuring Guide)
Fitted hat sizes are head circumference in inches ÷ π. Measure your head in 30 seconds, convert 52–64 cm to US/UK fitted and S–XXL sizes, and learn the fedora-era logic behind the eighths.
2026-07-05
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Image Tools · explainer
JPEG vs PNG vs WebP: Which Image Format to Use (and How to Shrink Files 90%)
JPEG for photos, PNG for screenshots and transparency, WebP for the web at 25–35% smaller. How each format works, the conversion mistakes that ruin images, and the resize-then-compress workflow that cuts files by 90%.
2026-07-05
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File Converters · explainer
JSON vs YAML vs XML: Which Data Format for Which Job
APIs speak JSON, humans edit YAML, legacy systems demand XML. How the three formats differ, when each wins, the Norway problem, and how to convert between them without losing data.
2026-07-05
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Size Converters · how-to
Kids' Shoe Sizes by Age: US, UK, EU Charts — and the 13C-to-1Y Mystery
US kids' sizes run 2C–13.5C then restart at 1Y (which is BIGGER). Get the full chart with ages and cm, the measuring method, growing-room rules, and the youth-to-women's trick.
2026-07-05
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PDF Tools · how-to
How to Merge, Split and Rotate PDFs Without Uploading Them Anywhere
PDF tools are where people upload their most sensitive documents — contracts, IDs, tax forms. How browser-based merging and splitting works, why it's lossless, and the workflows for the four most common PDF fixes.
2026-07-05
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Text Tools · explainer
camelCase vs snake_case vs kebab-case: Which Naming Case Goes Where
JavaScript uses camelCase, Python snake_case, URLs and CSS kebab-case, classes PascalCase, constants CONSTANT_CASE. The full convention map, why URLs prefer hyphens, and how to convert between them.
2026-07-05
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Generators · explainer
How Strong Is a Password, Really? Entropy Explained (Length Beats Complexity)
Password strength is measured in entropy bits: length × log₂(alphabet size). Why a 16-character lowercase password beats an 8-character symbol soup, what NIST actually recommends, and how to generate passwords that hold up.
2026-07-05
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Date & Time · explainer
Unix Timestamps Explained: Seconds vs Milliseconds, UTC and the Year 2038
A Unix timestamp counts seconds since 1 January 1970 UTC. How to convert one to a date, tell seconds from milliseconds at a glance (10 vs 13 digits), avoid the 1970-bug, and what actually happens in January 2038.
2026-07-05
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Color Tools · explainer
WCAG Color Contrast Explained: The 4.5:1 Rule Without the Jargon
WCAG AA requires 4.5:1 contrast for normal text and 3:1 for large text and UI — the standard cited by the EU Accessibility Act. What the ratio means, how to check it, and how to fix failing brand colors.
2026-07-05
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Audio & Video · explainer
WAV vs MP3: Lossless, Lossy, and Why Converting MP3 to WAV Doesn't Improve Anything
WAV stores every sample (~10 MB per stereo minute); MP3 discards what you're unlikely to hear at a tenth the size. When each format wins, why MP3→WAV can't restore quality, and how browser audio tools work locally.
2026-07-05
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Size Converters · explainer
Bra Size Conversion and Sister Sizes: US, UK and EU Explained
A US 34DD is an EU 75E and a FR 90E — and 36D holds exactly the same cup volume. Learn how band and cup systems convert, how to measure, and how sister sizes fix bras that almost fit.
2026-07-04
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Unit Converters · how-to
Celsius to Fahrenheit: Formula, Charts for Weather, Fever and Ovens
°F = °C × 9/5 + 32. The complete guide: exact formula, mental shortcut, charts for weather, fever thresholds, oven temperatures and world records — plus Kelvin and the history of both scales.
2026-07-04
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Unit Converters · how-to
Cups to mL and Grams: The Baking Conversion Guide That Actually Works
1 US cup = 236.59 mL — but an Australian cup is 250 mL and a Japanese cup is 200 mL. Get the cup-systems table, cups-to-grams for common ingredients, and why weighing beats scooping.
2026-07-04
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Calculators · explainer
How EMI Is Calculated: The Exact Formula Banks Use (With Worked Examples)
EMI = P·r·(1+r)ⁿ ÷ ((1+r)ⁿ−1). See the formula worked step by step, why early payments are mostly interest, the flat-rate trap, and how tenure changes total interest.
2026-07-04
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Unit Converters · how-to
Kg to Lbs Conversion: Formula, Charts and the 2-Second Mental Trick
1 kg = 2.2046 lbs exactly. The complete guide: formula, history, charts for body weight, gym plates, luggage and newborns, sports weight classes, common mistakes and FAQs.
2026-07-04
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Unit Converters · explainer
MB vs GB Explained: Why a 1 TB Drive Shows Only 931 GB
1 GB = 1,000 MB by the decimal standard, but Windows counts in binary. The complete guide: the full unit ladder from bit to quettabyte, missing-space tables, Mbps vs MB/s, phone storage and the law.
2026-07-04
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Calculators · how-to
How to Calculate Percentages: All 3 Forms, Fast Tricks and Real Examples
Every percentage problem is one of three forms. Learn all three formulas, the X%-of-Y = Y%-of-X swap trick, reverse percentages for sale prices, and the mistakes that trip everyone up.
2026-07-04
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Size Converters · how-to
How to Measure Your Ring Size at Home (US, UK, EU Charts Included)
Measure your ring size with a strip of paper in two minutes: circumference in mm IS your EU size, and US 7 = UK N = EU 54.4. Full conversion chart, secret-sizing tips for proposals, and the mistakes to avoid.
2026-07-04
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Unit Converters · explainer
How Many Miles Is a 5K, 10K, Half and Full Marathon? (+ Pace Charts)
A 5K is 3.11 miles, a 10K is 6.21, a half marathon 13.11 and a marathon 26.22 miles (42.195 km). Get finish-time pace charts, treadmill speed conversions and the 1908 story behind 42.195.
2026-07-04
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Size Converters · explainer
Shoe Size Conversion: US, UK, EU and cm — and Why Brands Never Quite Agree
A US men's 9 is UK 8, EU 42.5 and 26.5 cm — usually. Get the men's and women's charts, the barleycorn/Paris-point history behind the chaos, and the foot-measuring method that beats every chart.
2026-07-04