Power Converter
Type a number once — see it in every power unit instantly.
Enter a number to see it in every unit.
All units at once
| Unit | Value |
|---|---|
| Watt (W) | — |
| Milliwatt (mW) | — |
| Kilowatt (kW) | — |
| Megawatt (MW) | — |
| Horsepower (hp) | — |
| Metric horsepower (PS) | — |
| BTU per hour (BTU/h) | — |
| Foot-pound per second (ft·lb/s) | — |
| Gigawatt (GW) | — |
| Ton of refrigeration (RT) | — |
Why hp, PS, and kW never quite line up
Power ratings come from three different traditions that all still show up on the same spec sheet. Car engines are marketed in horsepower (hp) in the US and UK, in metric horsepower (PS) across most of Europe, Japan, and Korea, and increasingly in kilowatts (kW) because EU type-approval and electric-vehicle specs require it. Household appliances and pumps are usually rated in watts or hp on the nameplate. Air conditioners and furnaces are rated in BTU/h. None of these describe different physical quantities — they're all rates of energy transfer — but converting between them by memory is where most spec-sheet mistakes happen, especially between hp and PS, which look interchangeable and aren't quite.
How to use it
- Enter the number you have — for example the hp figure on an engine spec, or the wattage on an appliance label.
- Set From to the unit that number is already in, and To to the unit you want. The swap button (⇄) flips both at once.
- Read the highlighted result, or scroll the table below to see the same value expressed in all seven units simultaneously.
The math: why hp ≠ PS
Every conversion here goes through watts (W) as the common base, and each factor comes from an exact definition rather than a rounded estimate. Mechanical horsepower (hp) was defined by James Watt from horses turning a mill, standardized as exactly 550 foot-pounds of work per second — which works out to 745.6998715822702 W. Metric horsepower (PS, German Pferdestärke, also written cv or hp(M)) is defined instead as 75 kilogram-force-meters per second, using standard gravity (9.80665 m/s²), which works out to exactly 735.49875 W. Because the two definitions start from different base units (imperial foot-pounds vs. metric kilogram-force), they land about 1.39% apart — close enough to confuse, far enough to matter on a spec sheet.
Worked examples
Reference: exact conversion factors to 1 W
| Unit | 1 unit in W | Typical use |
|---|---|---|
| Watt (W) | 1 (base) | SI unit, electronics, small appliances |
| Kilowatt (kW) | 1,000 | Motors, generators, EV powertrains |
| Megawatt (MW) | 1,000,000 | Power plants, industrial turbines |
| Horsepower (hp) | 745.6998715822702 | US/UK engines, pumps, power tools |
| Metric horsepower (PS) | 735.49875 | EU/Japan/Korea car specs |
| BTU per hour (BTU/h) | 0.29307107017222222 | Air conditioners, furnaces, HVAC |
| Foot-pound per second (ft·lb/s) | 1.3558179483314004 | Physics and mechanics problems |
Common mistakes
- Treating hp and PS as the same number. They're close (about 1.4% apart) but a "300 PS" engine is not a "300 hp" engine — it's closer to 296 hp.
- Confusing power with torque. Engine specs also list torque (in N·m or lb-ft), a different physical quantity — this tool converts power units only, not torque.
- Assuming rated hp equals electrical watts on a motor nameplate. A motor's hp rating describes mechanical output; the electrical input in watts is higher due to motor efficiency losses, so don't use the hp-to-watt conversion alone to size a circuit breaker.
- Mixing up BTU (energy) with BTU/h (power). BTU/h is a rate — power — while a plain BTU is a unit of energy, the same way watts and watt-hours are not interchangeable.
What this tool doesn't do
This is a unit converter, not an efficiency calculator — it converts the number you type at face value and can't account for motor efficiency, drivetrain losses, or an engine's real-world output versus its rated figure. For electrical safety work (breaker sizing, wiring, generator loads), always use the equipment's actual nameplate ratings and consult a qualified electrician; this tool is for quick comparisons, not code compliance.
Sources & further reading
- NIST — SI units, including the watt as the unit of power
- NIST Reference on Constants, Units and Uncertainty — official unit definitions and conversion factors
- U.S. Department of Energy — appliance and motor power ratings in watts and BTU/h
- ISO — ISO 80000 standards covering quantities and units such as power
Frequently asked questions
How do I convert horsepower to kilowatts?
Multiply horsepower by 0.7457 to get kilowatts (1 hp = 0.7456998715822702 kW exactly, since mechanical horsepower is defined as 550 foot-pounds per second). For example, a 300 hp car engine is about 223.71 kW, and a 10 hp motor is about 7.46 kW. To go the other way, divide kilowatts by 0.7457 — a 150 kW electric motor is roughly 201.15 hp.
What's the difference between hp and PS (metric horsepower)?
hp is the mechanical (imperial) horsepower used in the US and UK, equal to exactly 745.6998715822702 W. PS (Pferdestärke, also called cv or hp(M)) is the metric horsepower common in Europe, Japan, and Korean car specs, equal to exactly 735.49875 W. The two are close but not identical: 1 PS ≈ 0.9863 hp, and 1 hp ≈ 1.0139 PS. A car rated at 100 PS is about 98.63 hp — a small but real gap that matters when comparing specs across regions.
How many watts does a horsepower motor draw?
1 mechanical horsepower equals 745.6998715822702 W, so a 1.5 hp pool pump or shop motor is rated at roughly 1,118.5 W (about 1.12 kW) of mechanical output — its actual electrical draw will be somewhat higher because motors aren't 100% efficient. Appliance and tool nameplates often list hp instead of watts, so converting lets you compare against a household circuit's wattage limit or an inverter/generator's rated output.
How does BTU/h relate to watts and horsepower?
BTU/h (British thermal units per hour) measures heating and cooling power, most often seen on air conditioner and furnace ratings. 1 BTU/h equals 0.29307107017222222 W. Air conditioners are commonly sold by "tons" of cooling, where 1 ton = 12,000 BTU/h ≈ 3.517 kW — useful when comparing a US-spec AC rated in BTU/h against a unit rated in kW or hp elsewhere.
Is my input sent to a server?
No. This power converter runs entirely in your browser — the number you type is never uploaded anywhere. The only thing saved is your last chosen unit pair (for example horsepower to kilowatts), kept in your browser's local storage so it's ready next time. The value itself is not stored.