EMBEDDED TOOL
Resistor Power (Wattage) Calculator
Calculate resistor power dissipation and get a suggested safe wattage rating.
Power dissipated
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Suggested resistor rating
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About this tool
Calculate how much power a resistor dissipates from any two of voltage, current, resistance, or power — and see a suggested standard resistor wattage rating with safety headroom, so you don't pick an underrated part that overheats.
Frequently asked questions
- Why does the suggested rating include headroom?
- Running a resistor right at its rated wattage shortens its life and risks thermal drift or failure, so this tool suggests the next standard rating (1/8W, 1/4W, 1/2W, 1W, 2W...) above roughly double the calculated dissipation — a common rule of thumb for reliable long-term operation.
- What formula does this use?
- Power is P = V × I, which is equivalent to P = I²R or P = V²/R — whichever pair of values you provide, the tool fills in the rest using Ohm's Law first.
- Is this the same as the Ohm's Law calculator?
- It solves the same underlying equations, but this tool is focused specifically on power dissipation and picking a safe wattage rating, including when you already know the power and resistance.