Motor Power Calculator
Convert between motor input power, shaft output power and horsepower.
About Motor Power Calculator
A motor nameplate states shaft output, not electrical input, so input power is always higher by the efficiency factor. Those losses become heat that the enclosure and ventilation must remove. Confusing nameplate kW with electrical demand undersizes supply cables and switchgear by around 10 per cent.
Formula
Motor Power
Input = √3 V I cos φ; shaft output = input × efficiency
- shaft power
- Mechanical power delivered, the motor nameplate rating
- losses
- Difference between input and output, dissipated as heat
Worked example
With the default values below, Motor Power Calculator returns Shaft Output Power of 9.7596. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Supply voltageminimum 1 V
- 400 V
- Full-load currentminimum 0 A
- 18 A
- Power factoraccepts 0.01–1
- 0.86
- Motor efficiencyaccepts 0–100 %
- 91 %
- Phasesone of Single phase, Three phase
- Three phase
Results
- Shaft Output Power
- 9.7596 kW
- Electrical Input Power
- 10.7249 kW
- Shaft Power
- 13.088 hp
- Losses as Heat
- 0.9652 kW
- Annual Energy at Continuous Duty
- 93,950 kWh
Step by step
- 1Values used
- 2Motor Power
- 3Shaft Output Power= 9.7596 kW
- 4Electrical Input Power= 10.7249 kW
- 5Shaft Power= 13.088 hp
- 6Losses as Heat= 0.9652 kW
- 7Annual Energy at Continuous Duty= 93,950 kWh
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Motor Power calculated?
Input = √3 V I cos φ; shaft output = input × efficiency A motor nameplate states shaft output, not electrical input, so input power is always higher by the efficiency factor. Those losses become heat that the enclosure and ventilation must remove.
Why does Motor Power matter?
Confusing nameplate kW with electrical demand undersizes supply cables and switchgear by around 10 per cent.
What values do I need to enter?
This calculator takes 5 inputs: Supply voltage, Full-load current, Power factor, Motor efficiency, Phases. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.