Enter any two known values — voltage, current, resistance, or power — and we'll solve for the rest.
Fill in Voltage and Current for the fastest solve — the calculator uses whichever two fields have valid numbers.
Ohm's Law is the foundation every other electrical calculation on this site builds on — wire sizing, breaker sizing, and battery runtime all trace back to these four relationships. Type any two values and the rest follow automatically.
Ohm's Law is one of the first things taught in any electronics course because nearly every other electrical calculation — wire sizing, breaker selection, battery runtime — ultimately reduces to these four variables. Keeping a mental model of the relationship (raise resistance, current drops; raise voltage, current rises) helps you sanity-check a spec sheet at a glance, before ever opening a calculator.
Voltage and current are the easiest to know from a nameplate or meter reading — filling those in solves for resistance and power automatically.
This is the pure resistive (DC) form. For AC circuits with motors or capacitors, impedance replaces resistance and the numbers will be approximate.
This solves the DC/resistive form of Ohm's Law. AC circuits with motors, capacitors, or inductors introduce reactance, where impedance replaces simple resistance — the numbers here will be a reasonable approximation for mostly-resistive AC loads but not exact for heavily inductive ones.