Electronics & Circuits Calculators
The everyday bench tools for building circuits, decode a resistor's color bands or a capacitor's code, size an LED resistor, work out a voltage divider or RC filter, design a 555 timer, look up a wire gauge, and estimate battery life. Standard formulas and reference tables, running entirely in your browser.
- Resistor Color Code Calculator Pick the color of each band to read a resistor's value and tolerance, with a live picture of the resistor as you go.
- LED Resistor Calculator Enter your supply voltage, the LED's forward voltage and its current to get the exact series resistor, plus the nearest standard value and its power.
- Voltage Divider Calculator Enter the input voltage and the two resistors to get the divider's output voltage, the current it draws and the power it dissipates.
- Capacitor Code Calculator Enter a ceramic capacitor's printed code
- Wire Gauge (AWG) Calculator Choose an AWG size to see its diameter, cross-section, copper resistance per length and typical current rating.
- RC Time Constant & Filter Calculator Enter a resistance and capacitance to get the RC time constant and the filter's cutoff frequency.
- 555 Timer Calculator Enter your resistors and capacitor to get the 555's output frequency and duty cycle
- Battery Life Calculator Enter your battery capacity and the device's current draw to estimate how long it will run.
- SMD Resistor Code Calculator Type the number printed on a surface-mount resistor to read its resistance, handles 3-digit, 4-digit, EIA-96 and R-notation markings.
- LC Resonant Frequency Calculator Enter an inductance and capacitance to get the LC circuit's resonant frequency and its characteristic impedance.
- Ohm's Law Calculator Enter any two of voltage, current, resistance and power, and the calculator fills in the other two using Ohm's law.
- Series & Parallel Resistor Calculator Enter a list of resistor values and get the total resistance both in series
- Series & Parallel Capacitor Calculator Enter a list of capacitor values in µF and get the total capacitance both in parallel
- Reactance Calculator (Xc & Xʟ) Enter a frequency and a capacitance or inductance to get its reactance, the frequency-dependent AC opposition in ohms.
- Decibel (dB) Calculator Convert a ratio to decibels or decibels to a ratio, for power
- Voltage Drop Calculator Voltage drop = 2 × current × the wire's resistance-per-metre × the one-way run length
From color bands to working circuits
Two things dominate the electronics bench: reading component markings and applying a handful of formulas. The resistor color code and 3-digit capacitor code pack a value into a few bands or digits, and these tools decode them instantly (with a live picture of the resistor). The rest is Ohm's law and a few standard relations, the series resistor an LED needs, how two resistors divide a voltage, the time constant and cutoff of an RC pair, and the frequency of a 555 timer, each shown with the equation so the tool teaches as it calculates.
Everything runs in your browser, so it's fast, private and works offline at the bench. One safety note: the wire-gauge current ratings are conservative guidelines, and anything involving mains voltage or building wiring must follow your local electrical code. For the underlying theory, Ohm's law, energy and the resistor/capacitor networks, see the Physics category.
Frequently asked questions
Are these electronics calculators accurate?
Yes. They use the standard tables and textbook formulas: the IEC 60062 resistor and capacitor color codes, the AWG diameter equation and copper resistivity, the NE555 timer equations, and Ohm's law. The data was cross-checked against IEC, manufacturer datasheets and NEC references.
Do these replace a datasheet or electrical code?
No. They're design aids for hobby and learning use. For anything involving mains voltage, building wiring or safety-critical current ratings, always follow your local electrical code and the component datasheets, and consult a qualified professional.
Is my data uploaded?
No. Every tool runs entirely in your browser, nothing is sent to a server, and they work offline.