Power units: overview and conversion factors
Watts, kilowatts, PS and horsepower – cars, machinery and electrical engineering
Power describes the amount of energy converted per unit of time. TheSI base unit of power is the watt (W), named after James Watt, the Scottish engineer who decisively advanced the steam engine. 1 watt = 1 joule per second (W = J/s). You encounter watts every day on electrical devices: an LED bulb uses 5–15 W, a vacuum cleaner 1,000–2,500 W, an electric stove 2,000–4,000 W. On a larger scale, kilowatts (kW = 1,000 W) and megawatts (MW = 1,000,000 W) are used.
The metric horsepower (PS) is a historical power unit that James Watt introduced to compare the output of his steam engines with the working power of horses. Metric horsepower is defined as the power needed to lift 75 kilograms at a speed of 1 metre per second: 1 PS = 75 kp·m/s = 75 × 9.80665 W = 735.49875 W. German vehicle registration documents state power in kW, though it is still commonly referred to as PS in everyday speech. 1 kW ≈ 1.36 PS.
The British-American horsepower (HP) differs from the metric PS: 1 HP = 550 ft·lbf/s = 745.6999 W – about 1.4% more than 1 PS (735.5 W). In the US car market, engine power is stated in HP. When comparing US vehicle data, you need to account for this difference: a 400-HP engine equals about 405.5 PS or 298.3 kW.
In the field of renewable energy, kilowatts and megawatts play a central role. A typical residential solar installation has 5–15 kW of peak power (kWp). A modern wind turbine generates 2–6 MW. Germany’s total electricity demand is around 60–80 GW (gigawatt = 1,000,000 kW) on annual average, with peak load exceeding 80 GW in winter. Large power plants are measured in gigawatts – a nuclear power plant has a rated output of roughly 1–1.6 GW.
In sport and fitness, power is measured in watts: a cyclist typically sustains 100–300 W, while a sprinter can briefly exceed 1,000 W. On an ergometer or smart trainer, power output is displayed live in watts. FTP (Functional Threshold Power) – the maximum power sustainable over 60 minutes – is an important training metric in cycling. With our power converter, you can quickly convert between all these units.
Want to convert only PS and kW directly? A dedicated PS-to-kW converter offers fast, bidirectional conversion with a reference table.