Ohm’s Law Calculator

About this calculator

This tool applies Ohm's law (V = I × R) and the related power formula (P = V × I) to a simple circuit: enter any two of voltage, current and resistance, and it solves for the missing one plus the power dissipated. Because the three quantities are locked together by the same equation, knowing any two always determines the rest — you never need to solve the algebra by hand.

Electronics hobbyists and students use it constantly when building circuits — picking a resistor value to limit current to an LED, checking whether a component will exceed its power rating, or verifying a circuit design before soldering it. Electricians and engineers use the same relationship to size wiring and troubleshoot circuits where a measured voltage and current don't match the expected resistance.