Energy worked example

Motor Energy Cost at 66% motor efficiency: a worked example

Suppose motor efficiency falls to 66%. This page works the full calculation at that level so you can see exactly which result moves and by how much. Calculate electric motor kWh and cost from horsepower, efficiency, load, runtime, and electric rate.

The inputs for this scenario

  • Motor horsepower: 25 hp (held at the documented default)
  • Motor efficiency: 66 % (the input this scenario stresses; the baseline uses 92)
  • Average load: 70 % (held at the documented default)
  • Runtime: 3,200 hr / yr (held at the documented default)
  • Electricity rate: 0.12 $ / kWh (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Input kW = horsepower × 0.746 × load ÷ efficiency.
  • Annual motor cost works out to 7,596 $ / yr at these inputs, and this is the headline figure for the scenario.
  • Motor input power works out to 19.78 kW at these inputs.
  • Annual energy works out to 63,297 kWh at these inputs.
  • Hourly cost works out to 2.37 $ / hr at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where motor efficiency sits at 92% and the headline result is 5,449 $ / yr, this scenario comes in 39.39% above the baseline at 7,596 $ / yr.
  • It converts a motor's nameplate horsepower, operating load, efficiency, and annual runtime into yearly energy use (kWh) and electricity cost at your utility rate. When the numbers land here, the stressed input is the lever to work; the walkthrough above shows exactly how much each output recovers as it climbs back toward the baseline.

Results at a glance

  • Annual motor cost: 7,596 $ / yr (headline result)
  • Motor input power: 19.78 kW
  • Annual energy: 63,297 kWh
  • Hourly cost: 2.37 $ / hr

Run it with your numbers

  • To rerun this with your own numbers, open the live Motor Energy Cost calculator, set motor efficiency to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.