Generator Efficiency

How to use this calculator

Generator efficiency is the ratio of useful electrical output to mechanical input: η = Pout / Pin. The difference, losses = Pin − Pout, is the power wasted as heat (copper I²R losses, core losses, friction, windage). Enter the input and output power and the efficiency, losses, and the input/output relationship appear live.

What it means in a real circuit

For 10 kW in and 9 kW out, efficiency is 90% and losses are 1 kW. A typical medium-sized generator runs at 85–95%; very small or very large units can differ. Efficiency peaks near full load and falls at light or heavy load because the fixed losses (core, friction) become a larger fraction. Use this to compare generators, to estimate fuel consumption (input energy), and to spot a machine that's running hotter or less efficiently than expected.