Ohm's Law Calculator

How to use Ohm's law

V = I × R. Know any two and the third follows: R = V ÷ I, I = V ÷ R. Power adds a fourth: P = V × I, which is also I²R and V²÷R.

Ohm's law examples

12 V, 4 A

3 Ω — 48 WA typical car accessory socket load.

2 A through 6 Ω

12 V — 24 W

230 V, 10 Ω

23 A — 5,290 WMains voltage: an element this low draws far more than a domestic circuit allows.

5 V, 220 Ω

0.0227 A (22.7 mA) — 0.11 WThe usual LED series resistor on a 5 V supply.