How Many Watts Equal One Horsepower?

One horsepower equals exactly 745.7 watts (more precisely, 745.699872 W). This is the mechanical horsepower definition, the one used for engines, motors, and most everyday comparisons.

Formula

The conversion formula is simple:

Watts = Horsepower × 745.699872

Where:

• Watts (W) – the SI unit of power, representing one joule per second.
• Horsepower (hp) – the imperial unit of power, originally defined by James Watt to compare steam engines to draft horses.

For most practical purposes, you can round to 746 W per horsepower. The exact number comes from the definition: 1 mechanical horsepower = 550 foot-pounds per second, which converts to 745.699872 watts.

Worked Example

Using the default value of 1 horsepower:

1. Start with the formula: Watts = 1 hp × 745.699872
2. Multiply: 1 × 745.699872 = 745.699872
3. Rounded to one decimal place: 745.7 watts

So a 2-horsepower motor draws approximately 1,491.4 watts (2 × 745.7). A 0.5-hp motor draws about 372.9 watts.

Why Are There Different Horsepower Values?

You might see several types of horsepower, and they are not all equal:

• Mechanical horsepower (hp) – 745.7 W, used for engines and motors in the US and UK.
• Metric horsepower (PS) – 735.5 W, used in Europe and Asia; it is defined as 75 kgf·m/s.
• Electrical horsepower – exactly 746 W, used for electric motors in some contexts.
• Boiler horsepower – 9,809.5 W, a historical unit for steam boilers.

When someone says “horsepower” without qualification, they almost always mean mechanical horsepower. If you are comparing European and American specs, check which unit is being used – a 100 PS engine is about 98.6 mechanical hp.

How to Convert Between Horsepower and Watts

To convert from horsepower to watts, multiply by 745.7. To go the other way, divide watts by 745.7.

Examples:

• 150 hp × 745.7 = 111,855 W (about 111.9 kW)
• 1,000 W ÷ 745.7 = 1.34 hp

For kilowatts, remember 1 kW = 1,000 W, so 1 hp ≈ 0.746 kW. A 5-hp motor is roughly 3.73 kW.

Common Mistakes and Misconceptions

One frequent error is using 746 W for all conversions. While that is close, it can cause small discrepancies in precise engineering work. Another is mixing up mechanical and metric horsepower – a 100 PS car is not the same as a 100 hp car.

Also, be careful with the difference between power and energy. Watts measure power (rate of energy use), while watt-hours measure energy. A 1-hp motor running for one hour consumes about 0.746 kWh of energy, not 746 kWh.

Why This Conversion Matters

Knowing the watt equivalent helps in several real situations:

• Electrical load calculations – when sizing generators, inverters, or circuits for motor-driven equipment.
• Comparing electric vs. gas tools – an electric lawn mower rated in watts can be compared to a gas mower rated in horsepower.
• Understanding utility bills – motors contribute to your electricity usage; converting to watts lets you estimate running costs.

For example, a 3-hp pool pump draws about 2,237 W. If you run it 8 hours a day, that’s roughly 17.9 kWh per day – a significant portion of a typical home’s electricity use.

Frequently Asked Questions

Is 1 horsepower really equal to one horse?

No. James Watt defined the unit based on a pony’s work rate, then estimated a horse could do 550 foot-pounds per second. In practice, a healthy horse can sustain about 0.7 to 1 horsepower for a short time, but not for hours. The unit is a convenient benchmark, not a biological constant.

How many watts is 5 horsepower?

5 hp × 745.7 W/hp = 3,728.5 watts (about 3.73 kW). This is the electrical input power for a motor running at full load, ignoring efficiency losses.

What is the difference between horsepower and brake horsepower?

Brake horsepower (bhp) is the power measured at the engine’s output shaft, before losses from the gearbox or alternator. Horsepower (hp) can refer to the same thing, but in some contexts it means power at the wheels. For practical purposes, the conversion to watts is the same.

How many watts does a 1-hp electric motor use?

At full load, a 1-hp motor consumes about 745.7 watts of mechanical output. However, because motors are not 100% efficient, the electrical input is higher – typically 850–1,000 watts depending on the motor’s efficiency rating.

Why do car engines use horsepower instead of watts?

Horsepower is a familiar marketing number that gives larger figures than kilowatts (e.g., 200 hp vs. 149 kW). Many countries now use kilowatts officially, but horsepower remains popular in the US and UK for consumer familiarity.

Can I convert watts to horsepower for a generator?

Yes, but note that generators are rated in both watts (continuous power) and surge watts. To run a 1-hp motor, you need a generator that can supply at least 746 W continuously, plus extra for startup surge – often 2–3 times the running wattage.

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in hp | Horsepower | hp | 1 | 0
out watts | Watts | W | hp * 745.699872 | 1