Electric Motors
Motor Power Factor Calculator
Motor Power Factor provides a checkable estimate of motor power factor. It is intended for scenario comparison, not as automatic approval of a component or installation.
Inputs for this calculation
Keep every entry on the units shown below.
Measurements and entries
Use nameplate data and measurements from the same load and supply condition. Do not combine a worst-case value with unrelated nominal data.
A denominator entry cannot be zero. Convert units once, retain the original reading, and verify the converted magnitude. For generator loading, use Generator Load Percentage Calculator.
- Real input power
- Default example: 11 kW. Enter real input power in kW.
- Apparent input power
- Default example: 14 kVA. Enter apparent input power in kVA.
From inputs to result
The displayed result follows PF = kW ÷ kVA × 100. The entered quantities are Real input power and Apparent input power.
For the example shown, motor power factor equals 78.57%. Treat that value as a demonstration, not a recommendation.
Calculate motor power factor from real input power and apparent input power. If you also need motor efficiency, continue with Motor Efficiency Calculator.
Transferring the result
Archive real input power and apparent input power with motor power factor. Identify the instrument, rating, or assumption behind each entry.
Pass motor power factor at its stored precision for dependent calculations. Keep a separate displayed value if reporting precision differs.
What the number means
Read Motor power factor as the outcome of this equation, not as automatic equipment approval. Compare it with nameplate, measured full-load, and actual duty-cycle values.
Save the raw entries before testing another scenario.
Common entry mistakes
Unit-prefix mistakes often dominate the arithmetic error.
Compare the magnitude with a quick independent estimate.
Checks before using the answer
Power factor varies with load.
Outside the entered variables, consider starting method, service factor, enclosure, and thermal duty. Document which effects were checked elsewhere in the analysis.
Record supply arrangement, speed, duty cycle, enclosure, and winding temperature.
Before relying on the answer
Can I select equipment from this number alone?
No. Compare the value with nameplate, measured full-load, and actual duty-cycle values and apply relevant equipment and installation requirements.
Should intermediate values be rounded?
Do not round between dependent calculations. Match the final display to the precision of the source data.
Why does the page show an input warning?
A zero denominator is undefined, so the affected field has a positive minimum.
Which source values should I use for Motor power factor?
Measured and rated values can represent different states. Separate shaft output power from electrical input power.
Which assumptions matter most here?
The result follows the displayed variables. Check starting method, service factor, enclosure, and thermal duty separately.