Ohm's Law Calculator

Calculate voltage, current, resistance and power — enter any two values (V = I × R, P = V × I).

What is Ohm's law?

Ohm's law says voltage equals current times resistance: V = I × R. Combined with power P = V × I, any two values give the other two — a 12 V supply across 6 Ω draws 2 A and dissipates 24 W.

Formulas

I = V ÷ R, R = V ÷ I
P = V × I = I² R = V² ÷ R

Check a resistor’s power rating is higher than the calculated power, with a safety margin.

Frequently asked questions

Does it work for AC circuits?

For purely resistive loads; inductive and capacitive loads need impedance.

What units are used?

Volts, amps, ohms and watts.

Is it free?

Yes.