Ohm's Law Calculator

It solves a simple DC or resistive circuit. Give it any two of voltage (V), current (I), resistance (R) and power (P), and it works out the remaining two using Ohm’s law and the power equations — no rearranging formulas by hand.

Ohm’s law states that voltage equals current times resistance: V = I × R. Rearranged, current is I = V ÷ R and resistance is R = V ÷ I. It describes how much current flows through a resistance for a given voltage, and is the foundation of nearly all circuit calculations.

Power is voltage times current: P = V × I. Combined with Ohm’s law that also gives P = I² × R and P = V² ÷ R, so the calculator can find power from whichever pair of values you enter — for example 120 V at 2 A is 240 W (230 V at 2 A is 460 W).

It works directly for DC and for purely resistive AC loads such as heaters and incandescent lamps. On AC circuits with motors, transformers or electronics the current and voltage fall out of step, so real power is V × I × power factor — the figure here is then the apparent power in VA, and you’d apply the power factor separately.

Whichever two you actually know. Choose the pair from the menu — voltage and current, voltage and resistance, current and power, and so on — then type the values. The calculator picks the right formulas for that combination and fills in the rest.

Use the Ohm’s law triangle — or the fuller Ohm’s law wheel that folds in the power formulas. Put V on top with I and R below it: cover the value you want and the layout tells you the sum — cover V and you get I × R, cover I and you get V ÷ R. A second triangle with P over V and I does the same for power.