Motor Energy Cost Calculator
Estimate electrical input power, annual energy use, and operating cost from shaft load and efficiency at that load.
Enter operating assumptions
Estimated motor energy cost
About this calculator
Estimate electrical input power, annual energy use, and operating cost from shaft load and efficiency at that load.
The efficiency must correspond to the entered shaft load. The calculator uses a constant efficiency and rate over the operating schedule.
Method and assumptions
Electrical input power = shaft horsepower × 0.7457 kW/hp ÷ motor efficiency fraction. Annual energy = input power × operating hours per day × operating days per year. Annual cost = annual energy × electricity rate.
Energy cost uses the entered electricity rate and operating schedule. It does not include demand charges, power-factor penalties, taxes, maintenance, or downtime unless the user includes them separately.
FAQs
Should I use nameplate horsepower as the actual shaft load?
Only if the motor is operating at that shaft load. Use a measured or engineering-estimated operating load when available; nameplate horsepower is a rating, not a continuous-load measurement.
Does the efficiency value remain constant at every load?
No. Motor efficiency changes with load and operating conditions. Enter efficiency data that matches the modeled shaft load and use manufacturer or test data where available.
Sources
Use motor manufacturer efficiency data at the evaluated load and the applicable utility tariff or energy invoice rate.