Energy calculator

Motor Energy Cost Calculator

Estimate motor electricity use from shaft load and operating efficiency. Enter the motor rating, actual load, matching efficiency, annual operating hours and energy price.

What this calculator does

  • Convert mechanical shaft demand into annual motor electricity use and cost.

Formula used

  • Shaft output = rated horsepower × 0.7457 × shaft load percentage ÷ 100
  • Electrical input = shaft output × 100 ÷ operating efficiency percentage
  • Motor loss = electrical input − shaft output
  • Annual energy = electrical input × annual hours
  • Annual energy cost = annual energy × energy price

Inputs explained

  • Rated Shaft Power: Mechanical horsepower rating on the motor nameplate.
  • Efficiency at Operating Load: Manufacturer efficiency or measured output/input ratio at this load.
  • Shaft Load: Mechanical output as a percentage of rated shaft power.
  • Annual Operating Hours: Yearly hours operating at the entered load and efficiency.
  • Energy Price: Applicable energy tariff for these operating hours.

How to use the result

  • Best suited to motor efficiency Comparison, constant duty energy budget.
  • Zero-load operation requires measured electrical input rather than this shaft-output model. Variable duty, drive losses and utility demand charges are excluded.

Current U.S. benchmarks

  • As of Jul 2026, industrial electricity averages 9.8 cents per kWh across the U.S. (EIA), up 4.7% from a year earlier. State averages range widely, so plants should confirm against their own tariff.
  • U.S. manufacturing runs at 75.7% of capacity (Federal Reserve, Aug 2026). New factory orders are up 8.5% year over year (Census).

Common questions

  • Can I use full-load nameplate efficiency at partial load? Only when it represents that operating point adequately. Obtain the manufacturer’s efficiency curve or a measured estimate when load differs substantially.
  • Does power factor replace efficiency? No. Efficiency relates useful shaft power to real electrical input. Power factor relates real and apparent electrical power.
  • Can the load exceed one hundred percent? This calculation is limited to rated output. Overload capability depends on the specific motor and operating conditions.
  • Why is zero shaft load rejected? A running unloaded motor can still consume electricity. Dividing zero shaft output by an assumed efficiency would incorrectly predict zero input.

Related guides

Last reviewed 2026-10-06.