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Power Converter

Convert power between watts, kW, MW, mechanical horsepower, metric horsepower (PS) and BTU/h with exact definitions and the formula for each pair.

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Formula:

≈ means the result was rounded to the chosen number of significant figures.

There are two horsepowers: mechanical hp = 745.69987 W (US, UK) and metric horsepower PS/ch/CV = 735.49875 W (continental Europe). Car specs in Europe usually use the metric one.

{value} in every unit

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Quick conversion table: {from} to {to}

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Common values

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Unit definitions

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How to use the power converter

  1. Type a power in Value. A decimal point or a decimal comma both work.
  2. Choose the starting unit in From and the target unit in To, for example kilowatt and mechanical horsepower (hp, imperial).
  3. The result appears as you type, with the full line below it (“1 kW ≈ 1.3410221 hp”). Copy puts that line on your clipboard.
  4. Swap units (⇄) reverses the conversion.
  5. Significant figures sets the rounding; “≈” marks a rounded value.

The page also lists the power in every unit, a quick table for the selected pair, everyday references (an LED bulb, a cyclist, a kettle, an air conditioner, a small car, a wind turbine) and the value of each unit in watts.

Which horsepower?

“Horsepower” is not one unit but several, and mixing them up is the most common error with car and engine specifications. This tool keeps them apart:

  • Mechanical horsepower (hp): 550 foot-pounds per second, the unit used in the United States and the United Kingdom. With the exact foot, pound and standard gravity, 1 hp = 745.69987158227022 W exactly.
  • Metric horsepower (PS, ch, CV, pk): 75 kilogram-force metres per second, used in continental Europe and Japan. 1 PS = 735.49875 W exactly (75 × 9.80665).
  • Electrical horsepower (hp(E)): exactly 746 W, found on electric motor nameplates.

The mechanical horsepower is about 1.4 % larger than the metric one: 100 PS is 98.63 hp, and 300 hp is 304.2 PS. When a European brochure says “150 hp”, it usually means 150 PS, which is 110.3 kW.

The legal unit on European vehicle registration documents is the kilowatt, which is why the most useful conversions are kW ↔ PS and kW ↔ hp: 1 kW ≈ 1.35962 PS ≈ 1.34102 hp.

Watts and BTU per hour

The watt is the SI unit of power: one joule per second. 1 kW = 1,000 W and 1 MW = 1,000,000 W.

BTU per hour measures heating and cooling power in North America. It uses the International Table BTU (1,055.05585262 J), so 1 BTU/h ≈ 0.29307107 W and 1 W ≈ 3.41214 BTU/h. A “12,000 BTU” air conditioner (one “ton of refrigeration”) delivers about 3.517 kW of cooling. That is thermal output, not the electricity it consumes, which is usually three to four times lower.

Power is not energy

Power is a rate, energy is an amount. A 2 kW heater running for 3 hours uses 6 kWh of energy. Kilowatts belong here; kilowatt-hours belong in an energy converter.

Frequently asked questions

How do I convert kW to hp?

Multiply by about 1.34102 for mechanical horsepower, or by 1.35962 for metric horsepower (PS). A 100 kW engine is about 134.1 hp or 136.0 PS.

What is the difference between hp and PS?

The hp is defined from feet and pounds (745.7 W), the PS from metres and kilogram-force (735.5 W). The PS is the smaller of the two, by about 1.4 %.

What does BHP mean?

Brake horsepower is the mechanical horsepower measured at the engine’s crankshaft, before losses in the gearbox and wheels. It uses the same 745.7 W unit.

How much power is one horse?

James Watt estimated that a mill horse delivered 33,000 foot-pounds per minute, which became the mechanical horsepower. A real horse can briefly produce much more, over 10 hp, but sustains less than 1 hp.

Why are the hp and PS factors not round numbers?

Because they come from older units: foot-pounds per second and kilogram-force metres per second. Both are nevertheless exact once the foot, the pound and standard gravity (9.80665 m/s²) are fixed.

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