Generator Power Calculator
Work out the electrical power, apparent power, and estimated engine power needed from your generator’s voltage, current and power factor.
What this calculator does
Generators are rated by the electrical power they can supply, but the engine driving them has to produce more mechanical power than the electrical output because of conversion losses. This calculator converts voltage, current and power factor into real and apparent electrical power, then estimates the mechanical power the engine needs to supply.
The formulas used
For single phase, apparent power (VA) = voltage × current. For three phase, apparent power (VA) = √3 × voltage × current. Real power (watts) = apparent power × power factor. Dividing real power by the generator’s efficiency gives an estimate of the mechanical engine power required.
This tool is for general electrical planning and education. Always size real generators with a safety margin and consult the manufacturer’s specifications and a qualified electrician for actual installations.