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Electrical power from V, I and R.
This calculator finds electrical power from the quantities you know. Choose whether you have voltage and current, current and resistance, or voltage and resistance, and it returns the power in watts and kilowatts.
Power is the rate at which electrical energy is converted to heat, light or motion, and knowing it is essential for sizing wiring, fuses, resistors and power supplies.
All three forms come from combining P = V × I with Ohm's Law (V = I × R); pick the one matching the values you have.
Use the one that matches your known values: P = V × I for voltage and current, P = I² × R for current and resistance, and P = V² ÷ R for voltage and resistance. All give the same answer for the same circuit.
Watts measure real power that does useful work; volt-amperes (VA) measure apparent power. In purely resistive circuits they are equal, but reactive AC loads make VA larger than watts.
Power (in kW) multiplied by running time (in hours) gives energy in kWh, which is what your electricity tariff charges for. Use the electricity cost calculator to turn watts into rupees.
When current flows through resistance, electrical energy is dissipated as heat at a rate P = I² × R. This is why undersized wires and overloaded resistors get hot and can fail.