V = I × R · P = V × I
Ohm's Law relates voltage, current and resistance in an electrical circuit. This calculator solves for any two unknown quantities from voltage (V), current (I), resistance (R) or power (P) — enter any two known values and the remaining two are calculated automatically. Useful for basic circuit analysis, component sizing and troubleshooting.
Results for guidance only. Verify against current standards and manufacturer data.
Not a substitute for engineering judgement or a licensed professional.
Ohm's Law states that current through a conductor is directly proportional to voltage and inversely proportional to resistance: V = I × R. Combined with the power formula P = V × I, six relationships can be derived to solve for any variable given two others. This calculator automatically selects the correct relationship based on which two values you provide.
A 12V DC circuit has a resistance of 4Ω. Entering V = 12 and R = 4 solves I = V/R = 3A and P = V × I = 36W. This applies to simple DC circuits — for AC circuits with reactive components, impedance (Z) replaces resistance (R) and power factor must be considered separately.