Horsepower to Watts Converter – HP to W and kW
Convert between horsepower (HP) and watts (W) in either direction. Supports electrical, mechanical and metric horsepower — just enter a value, pick the horsepower type and units, and get the result instantly.
Horsepower and Watts Conversion Tool
Horsepower to Watts Conversion Formula
Where:
- \(W\) — power in watts
- \(HP\) — power in horsepower
- \(F\) — conversion factor, which depends on the definition of horsepower used
The formula is a direct multiplication or division by a fixed factor. The factor changes with the horsepower standard: electrical horsepower is defined as exactly 746 W, mechanical (imperial) horsepower as about 745.7 W, and metric horsepower (PS, CV) as about 735.5 W.
Horsepower to Watts – Calculation Example
Example: an electric motor is rated at 1 electrical horsepower, and you want to know its power in watts.
\[ W = 1 \times 746 = 746 \, \text{W} \]
Result: 1 electrical horsepower equals 746 watts.
If the same motor were rated using metric horsepower instead, the result would be \(1 \times 735.4988 \approx 735.5\) W — about 1.4% less. This is why selecting the correct horsepower type matters.
How to Use the Calculator
- Enter the value you want to convert in the Enter value field.
- Select the appropriate Horsepower type: Electrical, Mechanical or Metric. Use Electrical for electric motor nameplates, Mechanical for US/UK engine ratings, and Metric for European PS or CV ratings.
- Choose the From unit (HorsePower or Watts).
- Choose the To unit (Watts or HorsePower).
- Read the converted value in the Result field. If both units are the same, the value is returned unchanged.
What Are Horsepower and Watts?
Both horsepower and watts measure power — the rate at which work is done or energy is converted. The watt is the SI unit of power: one watt equals one joule per second. It is the standard unit for electrical power worldwide and appears on everything from light bulbs to generators.
Horsepower is an older unit dating back to James Watt, who wanted to compare steam engines with draft horses. It survives mainly in the automotive, machinery and motor industries. The catch is that "horsepower" is not a single unit: there are at least three common definitions in use today, which is why this converter asks you to pick a type.
- Electrical horsepower — exactly 746 W, used for electric motors in the US.
- Mechanical (imperial) horsepower — 745.6999 W (about 550 ft·lbf/s), used for car and engine ratings in the US and UK.
- Metric horsepower (PS, CV) — 735.4988 W, used in Europe and much of Asia for vehicle ratings.
The differences are small — under 1.5% between types — but they matter when matching a motor to a load, checking an electrical supply, or comparing equipment specifications across regions. For instance, a 100 PS European car and a 100 hp American car do not have exactly the same power output.
Quick Reference Table
| Horsepower | Electrical (W) | Mechanical (W) | Metric (W) |
|---|---|---|---|
| 1 | 746 | 745.7 | 735.5 |
| 5 | 3,730 | 3,728.5 | 3,677.5 |
| 10 | 7,460 | 7,457 | 7,355 |
| 50 | 37,300 | 37,285 | 36,774.9 |
| 100 | 74,600 | 74,570 | 73,549.9 |
Practical Tips and Limitations
- Always check the nameplate. Electric motors in North America are rated in electrical horsepower (746 W each), so use the Electrical option for them. Car engines usually use mechanical or metric horsepower depending on the market.
- PS and CV are metric horsepower. If a European specification lists PS (Pferdestärke) or CV (cheval-vapeur), select Metric — they are all the same 735.4988 W unit.
- Input power vs. output power. Watts on a motor nameplate may refer to electrical input, while horsepower refers to mechanical shaft output. Since motors are not 100% efficient, converting between the two without accounting for efficiency can mislead. For AC circuits, our Real and Reactive Power calculator helps break down electrical power properly.
- Rounding. The calculator rounds results to 4 decimal places, which is more than enough for any practical engineering or comparison purpose.
- Related tools. To size wiring for a motor once you know its wattage, try the Wire Gauge calculator. For supply-side design, see the Single Phase Transformer calculator or the Zener Diode Resistor calculator for low-power voltage regulation.
Frequently Asked Questions
How do I convert horsepower to watts by hand without a calculator?
Multiply the horsepower value by the factor for its type: 746 for electrical, 745.7 for mechanical, or 735.5 for metric horsepower. For example, 15 mechanical hp is \(15 \times 745.7 \approx 11{,}186\) W, or about 11.2 kW. For a rough mental estimate, you can use 750 W per horsepower — the result will be within about 1.5% for any of the three definitions.
Why are there different types of horsepower, and which one should I use?
Horsepower was never standardized globally, so three definitions coexist. Use electrical (746 W) for North American electric motor nameplates, mechanical (745.7 W) for US/UK car and engine ratings, and metric (735.5 W) for European and Asian vehicle specs labeled PS, CV or ch. The units differ by less than 1.5%, but that gap matters when comparing engines across markets or matching a motor to a driven load.
How many watts are in 1 horsepower?
It depends on the definition: 1 electrical horsepower is exactly 746 W, 1 mechanical (imperial) horsepower is about 745.7 W, and 1 metric horsepower (PS/CV) is about 735.5 W. The often-quoted "746 watts" figure refers specifically to electrical horsepower, which is why it is the standard for electric motor ratings in the US.
How do I convert horsepower to kilowatts (kW)?
Convert to watts first, then divide by 1,000. For a metric example: 150 PS \(\times 735.5 = 110{,}325\) W \(\div 1000 = 110.3\) kW. Going the other way, a 100 kW motor equals \(100{,}000 \div 746 \approx 134\) electrical horsepower. Kilowatts are the SI unit and increasingly replace horsepower in vehicle specifications, especially for electric cars.
Does converting watts to horsepower account for motor efficiency?
No — this converter only changes units; it does not model losses. A motor's nameplate horsepower refers to mechanical shaft output, while its electrical input in watts is higher because motors are typically 75–95% efficient. For instance, a 1 hp motor drawing about 900 W of electricity still delivers only about 746 W of mechanical power. For sizing electrical supply or wiring, always base calculations on input power.
What is the difference between hp, PS, CV and bhp?
PS (Pferdestärke) and CV (cheval-vapeur) are simply the German and French names for metric horsepower — all equal 735.4988 W. Bhp (brake horsepower) measures an engine's output at the crankshaft on a dynamometer; depending on the region where it was measured, it is expressed in either mechanical or metric horsepower. When comparing specs, the safest approach is to convert everything to watts or kilowatts.
Is boiler horsepower the same as these horsepower types?
No. Boiler horsepower is a separate industrial unit equal to about 9,810 W, roughly 13 times larger than mechanical horsepower. It rates steam boilers by heat output, not mechanical shaft power. This converter handles only electrical, mechanical and metric horsepower, so do not use it for boiler ratings — doing so would give a result off by more than an order of magnitude.