Resistor Wattage Calculator
Find the power a resistor dissipates and get a safe recommended wattage rating with headroom for real-world use.
Why resistor wattage matters
Every resistor is rated for a maximum power it can safely dissipate as heat, commonly 1/8W, 1/4W, 1/2W, 1W, or higher. Running a resistor above its rated wattage causes it to overheat, drift in value, or fail.
The formula
Power dissipated is calculated as P = V² / R (equivalently P = I² × R or P = V × I). This calculator computes the actual power based on the voltage across the resistor and its resistance, then applies a safety margin — commonly 2x — since running a resistor near its maximum rated wattage shortens its life and increases heat in the surrounding circuit.
The suggested standard rating rounds up to the nearest common commercially available wattage. This tool is for general electronics planning and education; always check a component’s datasheet for its exact rating.