Calculate the power in an ohmic resistor
Find the power in watts from the resistance and either the current or the voltage. The calculator shows how the values are used in the calculation.
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Worked example
- Calculate from: Current and resistance
- Current: 2 A
- Resistance: 10 Ω
Result
Power
40 W
Working
- P = I² × R
(2 A)² × 10 Ω = 40 W
Choose current or voltage as the starting point
The power in a resistor describes how much energy is dissipated per unit of time. The calculator can be used when you know the resistance and either the current through it or the voltage across it.
The resistance is entered in Ω. If you choose current as the starting point, it is entered in A. If you choose voltage, it is entered in V. The result can be shown in W or kW. The calculation applies to an ohmic, resistive component.
Formulas for the power in the resistor
When the current is known, P = I² × R is used. The current is squared before multiplying by the resistance. When the voltage is known, P = U² / R is used. The voltage is squared, and the result is divided by the resistance.
The calculator finds the dissipated power. The permitted load of a component requires its own product data; if that is missing, the permitted load is unknown.
Example with 2 A through 10 Ω
The current is 2 A and the resistance is 10 Ω. First calculate 2² = 4. Then multiply by the resistance: 4 × 10 = 40 W. The full calculation is 2² × 10 = 40 W.