Automotive Calculators
Decode a tire size, check the speedometer error from a new set of wheels, work out road speed from RPM, size an engine or convert fuel economy between MPG and L/100km. Every tool is exact geometry or a definitional conversion, no estimates, and runs entirely in your browser.
- Tire Size Calculator Enter a tire size like 225/45R17 and get its true measurements, overall diameter, sidewall height, circumference and revolutions per mile.
- Tire Size Comparison & Speedometer Error Compare your current and a new tire size to see the diameter difference and exactly how much your speedometer will read off after the change.
- Gear Ratio & RPM Calculator Enter your gear ratio, final drive
- Engine Displacement Calculator Enter the bore, stroke and number of cylinders to get the engine’s displacement in litres, cubic centimetres and cubic inches.
- Compression Ratio Calculator Enter the swept volume and the clearance
- Horsepower & Torque Calculator Convert between horsepower and torque at any engine speed, enter two of the three and get the third, plus the metric kW and N·m equivalents.
- MPG & L/100km Converter Convert fuel economy between US MPG, UK MPG, litres per 100 km and kilometres per litre, with the US-vs-UK gallon difference handled correctly.
- Wheel Offset & Backspacing Calculator Convert between wheel offset
- EV Charging Time Calculator Enter your battery size, the charge levels and the charger power to estimate the charging time and energy added.
- Power-to-Weight Calculator Enter power
- Stopping Distance Calculator Enter your speed, reaction time and the tyre, road grip to get the reaction, braking and total stopping distances.
- 1/4-Mile ET & Trap Speed Calc Enter horsepower and weight to estimate the 1/4-mile elapsed time and trap speed.
- Fuel Cost Calculator Enter your trip distance, fuel economy and fuel price to see what the fuel will cost.
- Fuel Range Calculator Enter your tank capacity and fuel economy to see how far a full tank will take you.
- Tire Pressure Temperature Calculator Enter your set pressure and the temperature when you set it versus now to see the current pressure.
- Two-Stroke Fuel Mix Calculator For a two-stroke mix, oil = fuel ÷ the ratio number, so 5 litres of petrol at 50:1 needs 5000 ÷ 50 = 100 ml of oil.
- Trailer Tongue Weight Calculator Tongue weight percentage = tongue weight ÷ loaded trailer weight × 100, and it should land in the 10-15% range for safe, sway-free towing.
Frequently asked questions
Are these automotive calculators accurate?
Yes, every one uses exact geometry or a definitional unit conversion, not estimates. Tire dimensions come from the standard code formula, horsepower uses the exact HP = torque × RPM ÷ 5252 relationship, and fuel-economy conversions use the precise US and imperial gallon definitions. They’re Node-tested.
Do they handle metric and imperial units?
Yes. Tire sizes mix millimetres and inches (as the standard does); the displacement tool takes mm or inches; and the fuel-economy converter covers US MPG, UK MPG, L/100km and km/L, correctly accounting for the different US and UK gallons.
Is my data uploaded?
No. Every tool runs entirely in your browser, nothing is sent to a server, and they work offline.
Can I use these for modifications and fitment?
They’re a solid starting point for tire, gearing and wheel-fitment maths. Always verify clearances and manufacturer specifications on your actual vehicle before making changes.