How to Use the Power Calculator

The method selector at the top picks which pair of values the calculator expects next — choosing wrong just means switching it and re-entering, nothing gets lost.

Power has three faces depending on what you've measured — voltage and current, current and resistance, or voltage and resistance all get you there, and they're all the same underlying relationship viewed from a different angle.

P = V × I
P = I² × R
P = V² ÷ R

The second and third are just the first with Ohm's Law (V = IR) substituted in for whichever variable you don't have. This Power Calculator picks the right one automatically based on which two values you enter.