Calcmeister

Electric motor efficiency savings calculator

Enter the motor power, load, running hours and the efficiencies of the old and the new motor. The calculator shows the yearly saving and the payback time.

kW
%
h
%

From the nameplate or data sheet. Example 30 kW, 4-pole: IE1 90.7, IE2 92.3, IE3 93.6, IE4 94.9 %.

%
per kWh

Full price if the old motor still works, or only the price difference if it must be replaced anyway.

Saving per year
–
Energy saved
– kWh/year
Lower power draw
– kW
Payback
– years

    How the saving is calculated

    Both motors deliver the same mechanical power to the shaft. The more efficient motor draws less electrical power for it:

    Pshaft = Prated · load

    Saving (kW) = Pshaft ÷ ηold − Pshaft ÷ ηnew

    Saving per year = Saving (kW) · hours · electricity price

    Worked example

    A 30 kW pump motor runs 6,000 hours a year at 75 % load. Replacing an IE2 motor (92.3 %) with an IE4 motor (94.9 %) lowers the power draw by 0.67 kW and saves about 4,000 kWh per year. At 0.15 per kWh that is around 600 a year, so an investment of 1,500 pays back in 2.5 years.

    Typical efficiencies, 4-pole motors at 50 Hz

    Rated powerIE1IE2IE3IE4
    1.1 kW75.0 %81.4 %84.1 %87.2 %
    5.5 kW84.7 %87.7 %89.6 %91.9 %
    15 kW88.7 %90.6 %92.1 %93.9 %
    30 kW90.7 %92.3 %93.6 %94.9 %
    75 kW92.7 %93.9 %95.0 %96.0 %

    Minimum values from IEC 60034-30-1. Actual motors are often slightly better; use the data sheet values when you have them.

    When replacing pays off

    The higher the running hours and the electricity price, the faster a premium motor pays back. Motors that run more than 4,000 hours a year almost always justify IE3 or IE4. If a motor runs at varying load, a variable speed drive usually saves far more than the motor class alone, especially on pumps and fans.

    Questions and answers

    What are IE efficiency classes?

    IEC 60034-30-1 sorts motors into IE1 (standard), IE2 (high), IE3 (premium), IE4 (super premium) and IE5 (ultra premium) efficiency. In the EU, most new motors from 0.75 to 1,000 kW must meet at least IE3, and 75 to 200 kW motors IE4.

    How much can a better motor save?

    For a 30 kW motor running 6,000 hours at 75 % load, going from IE2 to IE4 saves about 4,000 kWh per year. Over a motor's 15 to 20 year life, the energy cost is far higher than the purchase price.

    Is the saving the same at part load?

    Efficiency drops below about 50 % load, and the gap between classes can change. For motors that run mostly at low load, a variable speed drive or a smaller motor may save more than a higher class.

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    Last reviewed: 2026-10-14. Results are estimates for planning. Check them before you rely on them for design, purchase or safety decisions.