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Horsepower to Kilowatts

Three horsepowers exist. This shows the two that matter.

Inputs
hp

The number of horsepower (mechanical) to convert.

Kilowatts
111.85kW
If that was metric hp (PS)
110.32kW
In PS, if it was mechanical hp
152.1PS
75 hp
55.93kW
150 hp
111.85kW
300 hp
223.71kW
500 hp
372.85kW
kW = hp × 0.7457 (mechanical) or × 0.7355 (metric PS)

1 hp = 0.7457 kW

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Multiply mechanical horsepower by 0.7457 for kilowatts, or metric horsepower (PS) by 0.7355. A 150 hp engine is 111.9 kW, or 110.3 kW if the figure was in PS.

How to use HP to kW Converter

  1. Enter the horsepower. From the spec sheet or the registration document.
  2. Check which definition. European figures are usually PS; American and British ones usually mechanical hp.

About converting horsepower to kilowatts

Horsepower is a unit invented for marketing and standardised afterwards, which is why more than one version of it exists. James Watt devised it in the 1780s to express the output of his steam engines in terms buyers understood — namely, how many draught horses the machine replaced — and the figure he chose was an estimate of sustained work rather than a measurement of any particular animal. The two definitions that matter today differ by about one and a half percent. Mechanical horsepower, used in Britain and the United States, is 745.7 watts. Metric horsepower, written PS in German-speaking markets and CV or pk elsewhere in Europe, is 735.5 watts. Both are quoted as "horsepower" in casual writing, so a car advertised at 300 in one market and 296 in another may be exactly the same engine described twice. Kilowatts avoid the ambiguity entirely, which is why European type approval and registration documents state power in kilowatts, often with PS shown alongside for familiarity. In several countries vehicle taxation bands are set against the kilowatt figure rather than either horsepower, which makes the conversion something owners need rather than an academic curiosity. It is worth knowing that a manufacturer figure is measured at the crankshaft under controlled conditions; power at the wheels is meaningfully lower once transmission losses are counted, typically by ten to fifteen percent.

Frequently asked questions

What is the difference between hp and PS?
Mechanical horsepower is 745.7 watts and metric horsepower — PS, from Pferdestärke — is 735.5, a difference of about 1.4%. A car quoted at 300 PS is 296 hp, which is why the same engine has slightly different numbers in different markets.
Why is kW used on European documents?
Because it is the SI unit and horsepower is not. EU type approval and vehicle registration documents state power in kilowatts, with PS often shown alongside for familiarity. Tax bands in several countries are set on the kW figure.
Where did horsepower come from?
James Watt defined it in the 1780s to sell steam engines against the draught horses they replaced, based on an estimate of what a horse could sustain lifting weight from a mine. It was a marketing unit from the beginning, which is why its definition needed standardising later.
Is there a third horsepower?
Several. Boiler horsepower, electrical horsepower and hydraulic horsepower all exist with different values, though only mechanical and metric appear on vehicle specifications. Electrical horsepower is defined as exactly 746 watts and turns up in motor ratings.

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