Free tool

Motor efficiency calculator: IE3 and IE4 savings

Enter your motor’s power, load and operating hours to see the energy and money saved by an IE3 or IE4 motor over your current one, with the payback time. Class efficiencies come from the tables of EU Regulation 2019/1781.

Saving per year

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How the calculation works

The new motor does the same work, that is, it delivers the same shaft power; what changes is the power drawn from the grid. The saving is the difference between the two, multiplied by the operating hours:

P shaft = rated power × load / 100
kWh/year = P shaft × operating hours × (1/η old − 1/η new)
Payback (years) = price difference / money saved per year

Assumption: efficiency at part load is taken as the rated (full-load) value. Real efficiency changes with load; if you enter the efficiency at your load from the datasheet, the tool uses it. Payback is simple payback: interest, energy price changes and maintenance differences are not included.

Example: The tool’s default example replaces a 22 kW 4-pole IE2 motor (91.6%) running at 75% load for 6,000 hours a year with an IE4 motor (94.5%). Shaft power is 16.5 kW and the power drawn falls from 18.01 kW to 17.46 kW; the saving is 3,317 kWh a year, or $398 at $0.12/kWh. A $1,500 price difference pays back in 3.8 years.

Where the class efficiencies come from

The IE2, IE3 and IE4 values are the 50 Hz minimum efficiencies of Tables 1, 2 and 3 in Annex I of Commission Regulation (EU) 2019/1781. For powers not in the tables the tool uses the regulation’s formula: between 0.12 and 200 kW, η = A·x³ + B·x² + C·x + D with x = log10(P / 1 kW) (coefficients from Tables 4 and 5), and a straight line between the 0.55 and 0.75 kW values. The table rows above 200 kW apply up to 1,000 kW. Above 1,000 kW or below 0.12 kW you enter the efficiency yourself. Classes are determined at rated output, rated voltage and 25 °C ambient temperature.

EU minimums (Annex I, point 1): since 1 July 2021, three-phase motors from 0.75 to 1,000 kW with 2–8 poles must be at least IE3, and those from 0.12 to below 0.75 kW at least IE2. Since 1 July 2023, motors from 75 to 200 kW with 2, 4 or 6 poles must be at least IE4, and Ex eb motors and single-phase motors at least IE2. Brake motors and explosion-protected motors are outside the IE4 requirement. These rules apply to motors placed on the market.

Sources

Commission Regulation (EU) 2019/1781 laying down ecodesign requirements for electric motors and variable speed drives, OJ L 272, 25.10.2019, Annex I (EUR-Lex). Checked 24 October 2026.
Commission Regulation (EU) 2021/341, OJ L 68, 26.2.2021: adds 60 Hz tables to 2019/1781 and leaves the 50 Hz tables and the dates unchanged (EUR-Lex). Checked 24 October 2026.
IEC 60034-30-1:2014, Rotating electrical machines, efficiency classes of line operated AC motors (IE code): definition of the classes.

Measuring real consumption

When average load and operating hours are estimates, so is the result. Measuring motor current, power and running time shows which motors are worth replacing; we describe this on our energy monitoring and machine data collection pages. For compressed air losses, use the compressed air leak calculator. All tools are on the tools page.

Frequently asked questions

Common questions

How is motor efficiency calculated?

Motor efficiency is the mechanical power delivered at the shaft divided by the electrical power drawn: η = P shaft / P input. A 22 kW motor at 75% load delivers 16.5 kW at the shaft; at 91.6% efficiency it draws 16.5 / 0.916 = 18.01 kW. The 1.51 kW difference is motor loss, turned into heat.

What are the IE2, IE3 and IE4 efficiency classes?

IEC 60034-30-1 defines motor efficiency classes: IE2 high, IE3 premium and IE4 super premium efficiency. The minimum efficiency of each class depends on rated power and number of poles. In the tables of EU Regulation 2019/1781, a 22 kW 4-pole motor at 50 Hz must reach 91.6% for IE2, 93.0% for IE3 and 94.5% for IE4.

Which motors must be IE3 or IE4 in the EU?

Under Regulation (EU) 2019/1781, since 1 July 2021 three-phase motors from 0.75 to 1,000 kW with 2, 4, 6 or 8 poles must be at least IE3, and those from 0.12 to below 0.75 kW at least IE2. Since 1 July 2023, motors from 75 to 200 kW with 2, 4 or 6 poles (except brake motors, Ex eb and other explosion-protected motors) must be at least IE4. The rules apply to motors placed on the market; they do not require replacing motors already in service.

How do you calculate the savings of a more efficient motor?

The shaft power stays the same, so the saving is the difference in power drawn: kWh/year = rated power × load × operating hours × (1/η old − 1/η new). In the tool’s example a 22 kW motor at 75% load for 6,000 hours a year saves 3,317 kWh a year going from IE2 to IE4; at $0.12/kWh that is $398 a year, and a $1,500 price difference pays back in 3.8 years.

Why does part-load efficiency matter?

Class values are rated (full-load) efficiencies. Motors usually run below full load and efficiency changes with load, dropping noticeably at low load. Regulation 2019/1781 requires manufacturers to state efficiency at 100%, 75% and 50% load. Enter the value from your datasheet and the motor efficiency calculator works at your own operating point.

What data do I need?

From the rating plate: rated power, number of poles (or speed) and efficiency class. Operating hours and average load can come from a meter or a current measurement. If the load is unknown, start with an estimate and correct it with a measurement.