Resistor Power Dissipation Calculator

About this calculator

Joule heating in a resistor follows P = I²R — power dissipated as heat rises with the square of current, so doubling the current quadruples the heat, not doubles it. The same power can equivalently be found from P = V²/R or P = V×I when voltage is known instead of current.

Electronics designers calculate this to pick a resistor whose printed power rating (commonly ⅛W, ¼W, ½W, 1W, or 2W for through-hole parts) comfortably exceeds the dissipated power, usually with at least a 2× safety margin, since a resistor run near its rated limit runs hot, drifts in value, and can fail. It's a routine check when sizing current-limiting resistors for LEDs or bleeder resistors in power supplies.