How to calculate ohm's law
V = I × R; P = V × I
Worked example. Voltage: 12 V.
Example inputs — Voltage (V) — 0 if unknown: 12; Current (A) — 0 if unknown: 2; Resistance (Ω) — 0 if unknown: 0; Power (W) — 0 if unknown: 0. Starting values are illustrative.
Enter any two values; the other two are solved for you.
From George Guju, founder of Calculyn · Educational calculator guidance, not professional advice.
How it works
Ohm's law links voltage, current and resistance (V = I × R); adding power (P = V × I) means any two of the four values determine the other two.
Assumptions & limitations
- Results are rounded for display.
Formula and assumptions reviewed October 2026 by the Calculyn team. How we build our calculators
Frequently asked questions
Does this work for AC circuits?
It works for resistive AC loads using RMS values, but not for circuits with significant capacitance or inductance.
What units should I use?
Volts, amps, ohms and watts. Convert milliamps to amps first (500 mA = 0.5 A).