Power Calculator
Enter any two of voltage, current, and power — leave the third field blank to calculate it.
Inputs
Result
Step-by-step working
Formula
- P = VI
- I = P/V
- V = P/I
P is power in watts, V is voltage in volts, I is current in amps.
About this calculation
Electrical power is the rate at which energy is transferred, and for a resistive load it is the product of the voltage across the component and the current through it. Enter any two of power, voltage and current and the calculator finds the third; the same quantity can also be written I²R or V²/R for a resistor.
Assumptions and limits
- It assumes a resistive load, or an AC load with a unity power factor. Reactive loads carry a power factor, and the real power they draw is lower than V × I.
- Power is treated as steady. A pulsed or varying load has an average and a peak rating, and the calculator returns neither of those on its own.
- The power dissipated in the connecting wires is not included.
A worked example
A load drawing 2 A from a 12 V supply dissipates P = V × I = 12 × 2 = 24 W, and that is the rate at which it converts electrical energy into heat, light or motion.
See also Ohm's Law and Decibel (dB).