The calculation, without hidden assumptions
Motor horsepower is output power, while supply current depends on the input power required to produce that output. This calculator first divides electric horsepower by the efficiency you enter, then uses the selected DC, single-phase or balanced three-phase power relationship. It does not substitute a code-table full-load current.
How to use this calculator
Choose DC, single-phase AC or balanced three-phase AC.
Enter horsepower, voltage and efficiency; AC modes also use the power factor you enter.
Review estimated input watts and current, then compare with the actual motor nameplate or authoritative table when sizing equipment.
Where people use it
- •Motor load sanity checks
- •Comparing current at different voltages
- •Learning how efficiency and PF affect input current
Example: 1 HP, 230 V, 90% efficiency, PF 0.85
One electric horsepower is 746 W output. At 90% efficiency the estimated input is about 828.9 W; single-phase current is then that input divided by 230 × 0.85.
What the result does not assume
- •Motor nameplate current and code-table values can differ from an ideal formula because of design, service factor, starting behavior and standards.
- •Do not size protection or conductors from this result alone.
Frequently asked questions
Why is efficiency included?+
Horsepower describes mechanical output. The motor must draw more electrical input power when efficiency is below 100%.
Why is PF included for AC?+
Real input power is voltage × current × PF for single phase, with the √3 factor for balanced three phase.
Is 746 W always one horsepower?+
This page uses electric/mechanical horsepower of approximately 746 W. Other horsepower definitions exist, so check the source unit.
Semantic next steps
Continue the calculation
These links move to a different input, formula or project stage rather than a keyword variation of this page.
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