1 Horsepower in Watts? Exact Conversion

One horsepower (mechanical) equals exactly 745.69987158227022 watts, usually rounded to 746 watts for everyday use. This page explains the conversion, the history behind the number, and how to convert between horsepower and watts for different types of horsepower.

Formula

The conversion formula is:

Watts = Horsepower × 745.69987158227022

• Watts (W) – the SI unit of power, equal to one joule per second.
• Horsepower (hp) – the unit of power originally defined by James Watt in the late 18th century to compare steam engines with horses.

The exact value comes from the definition: 1 mechanical horsepower = 550 foot-pounds per second. Converting that to metric units gives 745.69987158227022 watts.

Worked Example

Using the default value of 1 horsepower:

1. Start with the formula: Watts = Horsepower × 745.69987158227022
2. Plug in 1 hp: Watts = 1 × 745.69987158227022
3. Result: 745.69987158227022 watts, which rounds to 745.70 W.

So 1 hp equals 745.70 watts (rounded to two decimal places). For most practical purposes, you can use 746 W.

Why 746 Watts? The History of Horsepower

James Watt needed a way to sell his improved steam engines to miners and mill owners who were used to horses. He observed that a strong draft horse could lift 550 pounds one foot in one second. That became the definition of one horsepower: 550 ft·lb/s.

When the metric system later standardized power, the watt was defined as one joule per second. Converting 550 ft·lb/s to watts gives the exact number above. The 746 W figure is a convenient approximation that is accurate enough for most engineering and consumer applications.

Different Types of Horsepower

Not all horsepower is the same. The conversion factor depends on which type you are using:

• Mechanical (imperial) horsepower – 1 hp = 745.7 W. Used in the US and UK for engines and motors.
• Metric horsepower (PS) – 1 PS = 735.49875 W. Used in Europe and Asia for car engines. It is based on the power needed to lift 75 kg one meter in one second.
• Electrical horsepower – 1 hp = 746 W exactly. Used for electric motors in some contexts.
• Boiler horsepower – 1 hp = 9,809.5 W. Used to rate steam boilers.

When someone says “horsepower” without qualification, they usually mean mechanical horsepower. But always check the context, especially when comparing cars from different regions.

How to Convert Watts to Horsepower

To go the other way, divide watts by 745.7 (for mechanical hp). For example:

• 1,000 W ÷ 745.7 = 1.34 hp
• 2,500 W ÷ 745.7 = 3.35 hp
• 500 W ÷ 745.7 = 0.67 hp

This is useful when you have an appliance rated in watts and want to compare it to an engine rated in horsepower.

Common Mistakes and Misconceptions

• Using the wrong horsepower type – mixing up mechanical and metric horsepower gives about a 1.4% error. For a 200 hp engine, that is about 3 hp difference.
• Confusing power with torque – horsepower is a rate of doing work, while torque is a rotational force. They are related but not the same.
• Rounding too early – if you round 745.7 to 700, you get a 6% error. Always use 746 or 745.7 for accuracy.

Why This Conversion Matters

Knowing the watt equivalent helps when comparing engines to electric motors, understanding energy costs, or sizing generators and solar systems. For instance, a 10 hp motor draws about 7,460 watts of electrical power (ignoring efficiency losses). A typical household circuit is 15 amps at 120 volts, which is 1,800 watts – so a 10 hp motor would need a dedicated circuit.

When reading product specs, you may see power listed in both hp and kW (kilowatts). Since 1 kW = 1,000 W, 1 hp is about 0.746 kW. Many European car manufacturers now list power in kW instead of PS, so knowing the conversion helps compare with US specs.

Frequently Asked Questions

Is 1 horsepower really equal to one horse’s power?

No. James Watt’s estimate was based on a strong horse working continuously, but a typical horse can produce about 0.5 to 0.7 horsepower for sustained work, and can briefly produce much more. The unit is a standardised measure, not a biological constant.

What is the difference between hp and bhp?

Bhp (brake horsepower) is the power measured at the engine’s crankshaft before losses from the gearbox and drivetrain. Hp is a general term that can mean the same thing, but sometimes refers to power at the wheels (whp). Always check what the manufacturer means.

How many watts does a 1 hp electric motor use?

An electric motor rated 1 hp consumes about 746 watts of electrical power, but due to inefficiencies it may draw more – often around 900–1,000 watts. The nameplate rating is the mechanical output, not the electrical input.

Why do cars in Europe use PS instead of hp?

PS (Pferdestärke) is the German abbreviation for metric horsepower. It is a slightly different unit (735.5 W vs 745.7 W) that was adopted in continental Europe. Many countries now use kW as the official unit, but PS remains common in everyday car discussions.

How do I convert horsepower to kilowatts?

Divide the horsepower by 1.341 (since 1 kW = 1,000 W and 1 hp = 745.7 W, so 1 kW = 1.341 hp). For example, 150 hp ÷ 1.341 = 111.9 kW.

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in hp | Horsepower | hp | 1 | 0
out watts | Watts | W | hp * 745.69987158227022 | 2