Resistor Wattage Calculator

Your details

Choose which quantity to solve for. The two remaining inputs are used.
Current through the resistor in amperes. Use RMS current for AC circuits.
A
Resistance of the resistor in ohms.
Ohm
Known power dissipation in watts. Used only when solving for V, I, or R.
W
Optionally analyse a two-resistor series or parallel circuit. Voltage source drives both resistors.
Power dissipatedSafe (within 50 % derating)
1.2W

Heat dissipated by the resistor

Voltage12V
Current0.1A
Resistance120Ohm
Derated wattage needed2.4W
Recommended wattage rating3W
Rating utilization40%
40 %
Safe zone<50Marginal50-80Overloaded80+

Power dissipated: 1.2000 W - recommended rating: 3 W

  • The 50 % derating rule means you need a resistor rated at least 2.400 W; the nearest standard value is 3 W.
  • At 40.0 % of the rated wattage, this resistor will run cool and should last for decades under continuous use.
  • Circuit conditions: 12.000 V across 120.00 Ohm draws 0.1000 A (P = V x I = 1.2000 W).

Next stepTo reduce power dissipation, increase resistance or reduce the supply voltage. Use a heatsink for resistors above 1 W if the derating factor is tight.

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