kW to HP Calculator
One kilowatt is 1.341 horsepower. The only complication is that there are two horsepowers in circulation, and that a kW figure taken off an electricity bill is not the same quantity as the HP on a motor plate.
Inputs
| Project | Circuit ref | ||
| Prepared by | Date | ||
| Checked by | Date |
kW to HP Calculator · HP = kW / 0.7457 · EnergyCalcHQ · energycalchq.com
Preliminary calculation. The figures behind it are representative values for the stated conditions, not a substitute for the current edition of the standard or the manufacturer's published data. Verify before issuing for construction. Not a substitute for a qualified engineer or a protection study.
For page numbers, keep Headers and footers ticked under More settings in the print dialog.
The formula
HP = kW / 0.7457 = kW × 1.341
For metric horsepower — PS or CV, common on Indian and European motor plates — the divisor is 0.7355, so one kilowatt is 1.360 PS.
| Watts per unit | 1 kW equals | |
|---|---|---|
| Mechanical HP | 745.7 | 1.341 HP |
| Metric HP (PS, CV) | 735.5 | 1.360 PS |
The two differ by 1.4 %. It is invisible in an estimate and awkward when a delivered nameplate is being checked against an order.
The trap: input kW is not output HP
This is the direction where the conversion goes wrong most often.
A motor's HP is shaft output. A kW figure may be either output or input, and which one you have changes the answer:
- A motor plate marked 3.7 kW is stating shaft output. That is 5.0 HP, and the conversion is direct.
- A 4.24 kW figure measured at the supply, or read from a bill, is input. Convert that straight to HP and you get 5.7 HP for a motor that is a 5 HP machine — because you have converted the losses into horsepower too.
To go from measured input to shaft horsepower, take the efficiency out first:
HP = (kW input × efficiency) / 0.7457
Standard motor sizes, both ways
IS and IEC motors are built to a preferred series in kW, and the HP equivalents are the familiar numbers because the series was chosen to land near them:
| kW | HP (mechanical) | Usually sold as |
|---|---|---|
| 0.37 | 0.50 | 0.5 HP |
| 0.75 | 1.01 | 1 HP |
| 1.5 | 2.01 | 2 HP |
| 2.2 | 2.95 | 3 HP |
| 3.7 | 4.96 | 5 HP |
| 5.5 | 7.38 | 7.5 HP |
| 7.5 | 10.06 | 10 HP |
| 11 | 14.75 | 15 HP |
| 15 | 20.12 | 20 HP |
| 18.5 | 24.81 | 25 HP |
| 22 | 29.50 | 30 HP |
Note that none of them land exactly. A "10 HP" motor is a 7.5 kW machine delivering 10.06 HP, and a "3 HP" motor delivers 2.95. The kW figure is the real rating; the HP is the traditional label rounded to it.
When it matters which you quote
Specify in kW for anything you are buying, testing or protecting: it is what IS and IEC motor standards use, it removes the metric ambiguity, and it is the number the efficiency class is defined against.
Quote HP when you are talking to somebody who thinks in it — pump and compressor selection, vehicle engines, and most site conversations in India. There is nothing wrong with the unit. There is something wrong with two people using it to mean 745.7 and 735.5 without noticing.
For the current that motor will draw, the HP to amps calculator applies efficiency and power factor together, which is what actually sets the cable and the protection.
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