Ohm's Law Power Calculator

About this calculator

This calculator combines Ohm's law (V = I·R) with the power formula (P = V·I) to find electrical power, and can also solve for resistance, current, or voltage when any two of the four quantities are known — deriving relationships like P = I²R and P = V²/R along the way. These equations describe how voltage, current, resistance, and power relate in any DC circuit, from a single resistor to a full electrical load.

Electrical and electronics students working through circuit-analysis homework, hobbyists building Arduino or Raspberry Pi projects who need to size a resistor or check a component's power rating, and electricians verifying that a device won't exceed a circuit's wattage capacity use this. Enter any two known values — voltage, current, resistance, or power — to solve for the rest.