HP to kW Calculator
Convert motor and pump power between horsepower, kilowatts and watts — handy for sizing solar for well pumps, compressors and generators.
This is shaft/output power. A motor draws more input power than its rating — divide by its efficiency (typically 0.75–0.9) for electrical demand.
Quick answer
kW = HP × 0.7457. One metric horsepower (PS) = 0.7355 kW.
- 1 HP = 0.746 kW; 5 HP = 3.73 kW; 7.5 HP = 5.59 kW
- 1 PS (metric HP) = 0.736 kW
- A 1 HP motor that is 85% efficient draws about 0.88 kW from the supply
How this conversion works
1 HP (electric) = 746 W = 0.746 kW; 1 metric HP (PS) = 735.5 W.So kW = HP × 0.746. A motor’s electrical input = output ÷ efficiency, so a 1 HP motor at 85% efficiency draws about 0.88 kW.
Horsepower, kilowatts and what a motor really draws
Horsepower and kilowatts both measure power; 1 electric horsepower is 746 watts. Pumps, compressors and tools are often rated in HP, but to size solar, a well pump or a generator you need kilowatts — and then the input power, which is higher than the rated output because no motor is 100% efficient.
Worked example
A 1 HP well pump outputs 0.746 kW. At 85% efficiency it draws about 0.88 kW running — and several times that for a fraction of a second at start-up, which is what really sizes the inverter or generator.
Common motor sizes, converted
| Motor | Output | Electrical input @85% | Typical start surge |
|---|---|---|---|
| 0.5 HP (small pump) | 0.37 kW | 0.44 kW | ~1.3 kW |
| 1 HP (well pump) | 0.75 kW | 0.88 kW | ~2.6 kW |
| 1.5 HP (pool pump) | 1.1 kW | 1.3 kW | ~3.9 kW |
| 2 HP (compressor) | 1.5 kW | 1.8 kW | ~5.3 kW |
| 5 HP (farm/agri pump) | 3.7 kW | 4.4 kW | ~13 kW |
The surge column is why generator and inverter sizing is driven by starting current, not running watts — a 1 HP pump that runs happily on 1 kW needs roughly 3 kW available for the instant it starts.
Frequently asked questions
One electric horsepower is 0.746 kW (746 watts). Metric horsepower (PS) is slightly less, at 0.7355 kW.
Electric/mechanical HP is 746 W; metric horsepower (PS, common in Europe) is 735.5 W. They differ by about 1.4%.
No, it outputs 0.746 kW but draws more, because of motor losses. Divide by efficiency (0.75 to 0.9) for the electrical input, so roughly 0.83 to 0.99 kW.
Motors surge to several times their running power for a moment at start-up. Inverters and generators must handle that peak, not just the steady kW.
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Learn more
Sources & standards
This is a unit-conversion and motor-sizing tool, so its figures rest on SI definitions and motor standards rather than solar policy.
- NIST Special Publication 811 — Guide for the Use of the International System of Units (SI) — National Institute of Standards and Technology
Source for the exact 746 W-per-horsepower conversion factor used throughout the calculator. - ANSI/NEMA MG 1 — Motors and Generators — National Electrical Manufacturers Association
Defines standard motor horsepower ratings and nameplate conventions referenced in the worked examples. - IEEE 112 — Standard Test Procedure for Polyphase Induction Motors — Institute of Electrical and Electronics Engineers
Standard procedure behind the motor-efficiency figures used to convert rated output to electrical input. - NFPA 70 (National Electrical Code) — National Fire Protection Association
U.S. code basis for sizing conductors, generators and inverters to a motor's starting and running current.