Electronics calculators
Fast, practical answers for everyday circuit design. Enter your values, see the maths, and check the assumptions before choosing parts.
8 interactive tools · No sign-up · Works in your browserThese tools assume ideal components unless a note says otherwise. Use the actual component data sheets and check tolerances, power ratings and the limits of your source or controller. Calculations are intended for low-voltage learning and design estimates.
Ohm’s law & power
Find voltage, current, resistance and power from two known values.
P = V × I. Zero resistance and negative values are outside this simple model.
LED series resistor
Estimate resistance and resistor power for one indicator LED.
R = (supply − forward voltage) ÷ current. Choose a suitable standard value and check the LED and source ratings.
Voltage divider
Two resistors in series, measured at their midpoint.
Vout = Vin × R₂/(R₁+R₂). This assumes no load on the output; a connected load can change it.
Resistor networks
Add values separated by commas; compare series and parallel.
Use positive values only, for example 100, 220, 470. All resistors share the same two nodes in parallel.
Capacitor networks
Find equivalent capacitance in series or parallel.
Use positive values. The series result assumes ideal capacitors; voltage sharing depends on real leakage and tolerances.
RC time & cutoff
A first-order resistor-capacitor estimate.
τ = RC; cutoff = 1/(2πRC). At one time constant a simple charging capacitor reaches about 63% of the final change.
Frequency ↔ period
Switch between two views of a repeating signal.
f = 1/T, with period T in seconds. Applies to repeating signals.
4-band resistor decoder
Read two digits, a multiplier and tolerance.
Read from the end opposite the spaced tolerance band. Check markings if band order is unclear.
Keep learning
See the LED resistor worked guide, the Ohm’s law lesson, and the existing Tools page.
Worked example: Read our voltage divider guide to see how a connected load changes the calculator’s ideal result.