Power Converter (W, kW, hp, PS, BTU/h)

How the conversion works

Every unit on this page is defined by how many watts it represents. The watt is the SI unit of power, defined as one joule of energy per second. The input is converted to watts, then from watts into the target unit:

result = value × (watts per source unit) ÷ (watts per target unit)

Power describes a rate: how quickly energy is delivered or consumed. For the total amount of energy over time, see the energy converter.

Two kinds of horsepower

Car specifications routinely mix two units that both get called "horsepower" but differ by about 1.4%.

The metric unit goes by different names by country: PS (Pferdestärke) in Germany, CV (cheval vapeur) in France, pk (paardenkracht) in the Netherlands. They are all the same 735.49875 W.

The practical effect: a car advertised as "150 PS" in Germany is 147.9 hp in a UK review of the same car. The engine did not change, only the unit did. When comparing figures from different sources, check which horsepower is meant, especially near round numbers where the difference decides whether a car "makes 200 hp" or not.

Both are historical units originating from James Watt's comparison of steam engines to draft horses. The SI unit, the watt, is named after him and is increasingly used directly in engine specifications, particularly for electric vehicles.

Quick reference table

Typical power levels

Practical examples

Comparing car engines internationally

A German listing showing 150 PS, a UK review quoting 148 hp, and a spec sheet stating 110 kW all describe the same engine. Converting to kilowatts first removes the ambiguity entirely, which is why EU type approval documents state kilowatts as the primary figure.

Air conditioning and heat pumps

Cooling capacity is quoted in BTU/h in the US and kilowatts elsewhere. A 12,000 BTU/h unit is 3.5 kW. Note that this is thermal output, not electrical input: a heat pump with a coefficient of performance of 4 delivers 3.5 kW of heat while drawing under 0.9 kW of electricity.

Appliance energy costs

Multiply an appliance's power in kilowatts by hours of use to get kilowatt-hours, then multiply by your electricity rate. A 2 kW heater running 4 hours a day uses 8 kWh daily. Over a 90-day heating season that is 720 kWh.

Solar panels and generators

Solar installations are rated in kilowatts peak (kWp), the output under standard test conditions. Actual annual yield depends on location and orientation, typically 900 to 1200 kWh per kWp per year in central Europe. A 10 kWp system therefore produces roughly 9000 to 12,000 kWh annually.

Frequently asked questions

Is PS the same as horsepower?

Not exactly. 1 PS is 735.49875 W while 1 mechanical hp is 745.6999 W, so PS is about 98.6% of hp. A 150 PS engine is 147.9 hp.

How many watts is one horsepower?

745.6999 W for mechanical horsepower, 735.49875 W for metric horsepower (PS). Both figures are exact by definition of their respective units.

How do I convert kilowatts to horsepower?

Multiply by 1.341 for mechanical hp, or by 1.360 for metric PS. A 100 kW engine is 134.1 hp or 136.0 PS.

What is the difference between power and energy?

Power is the rate of energy transfer, measured in watts. Energy is the total transferred over time, measured in joules or kilowatt-hours. A 1 kW device running for 1 hour uses 1 kWh of energy.

How many BTU/h is a kilowatt?

3412.14 BTU/h. Dividing a BTU/h rating by 3412 gives the equivalent in kilowatts.

Why do electric cars list kilowatts instead of horsepower?

Because kilowatts are the SI unit and are used directly in electrical engineering, where motor output, battery capacity, and charging rates are all naturally expressed in watts or kilowatts. Many manufacturers still list horsepower alongside for familiarity.

Related converters

• Energy converter, for total energy rather than rate
• Force and torque converter, for the torque figures quoted alongside engine power
• All unit converters