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Resistor Power Calculator

Enter the resistance and either voltage or current to find the power dissipated.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

Power dissipated in a resistor follows Joule's law, calculated either from voltage as P = V² / R or from current as P = I² × R — both give the same wattage for a given resistance, since V = IR links them. Only voltage or only current is needed alongside the resistance value; the calculator fills in whichever formula applies.

Electronics engineers and hobbyists check this before finishing a circuit to make sure a resistor's power rating (commonly 1/8W, 1/4W, 1/2W, or 1W for through-hole types) is high enough for the current it will actually carry — undersizing it causes the resistor to overheat, discolor, or fail outright.

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