One Horsepower in Watts? Exact Answer

One horsepower equals exactly 745.69987158227022 watts (about 745.7 W). This is the mechanical horsepower definition, the one used for car engines, electric motors, and most machinery. If you see a power rating in hp, multiply it by 745.7 to get watts.

Formula

The conversion is a fixed constant, not a formula that depends on other variables:

P(W) = P(hp) × 745.69987158227022

• P(W) — power in watts (W)
• P(hp) — power in mechanical horsepower (hp)

The constant 745.69987158227022 is exact by definition: 1 mechanical horsepower = 550 foot-pounds per second, and 1 foot-pound per second = 1.3558179483314004 watts. Multiply 550 × 1.3558179483314004 to get 745.69987158227022.

Worked Example

Using the calculator defaults (1 hp):

1. Start with 1 hp.
2. Multiply by the conversion constant: 1 × 745.69987158227022 = 745.69987158227022 W.
3. Round to 2 decimal places: 745.70 W.

So a 1 hp motor produces about 745.7 watts of mechanical output power. A 2 hp motor gives 1,491.4 W; a 0.5 hp motor gives 372.85 W.

Why There Are Different Horsepower Values

Horsepower is not a single universal unit. The most common types are:

• Mechanical horsepower (hp) — 745.7 W, used in the US and UK for engines and motors.
• Metric horsepower (PS or CV) — 735.49875 W exactly, 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 — about 9,809.5 W, a historical unit for steam boilers.

When someone says “horsepower� without qualification, they almost always mean mechanical horsepower. But if you are comparing European and American specs, check which one is being used — the difference is about 1.4%.

Why 550 Foot-Pounds Per Second?

James Watt (1736–1819) needed a way to sell his improved steam engines. He observed that a strong draft horse could lift 550 pounds one foot in one second, and he defined that as one horsepower. That number became the standard in the English-speaking world.

The metric horsepower came later, based on the same idea but using kilograms and meters: lifting 75 kilograms one meter in one second. Both definitions are approximations of what a real horse can do — real horses vary, and a healthy horse can briefly produce far more than 1 hp, but sustain only about 0.7–1 hp for long periods.

How to Convert Horsepower to Watts in Practice

For quick mental math, use these rounded values:

• 1 hp ≈ 746 W (common in electrical engineering)
• 1 hp ≈ 0.746 kW
• 1 kW ≈ 1.34 hp

To convert:

1. Multiply hp by 745.7 for watts.
2. Divide watts by 745.7 for hp.
3. For kW, multiply hp by 0.7457.

Example: A 150 hp car engine produces 150 × 745.7 = 111,855 W = 111.9 kW. A 2.5 kW electric motor is about 2.5 / 0.7457 = 3.35 hp.

Common Mistakes and Misconceptions

• Using the wrong horsepower type: Metric hp (PS) is 735.5 W, not 745.7 W. Mixing them gives errors of about 1.4%.
• Confusing input power with output power: The hp rating of an electric motor is the mechanical output power. The electrical input power is higher because of losses (heat, friction).
• Rounding too early: If you round 745.7 to 746, the error is small but can accumulate in multi-step calculations.
• Forgetting that “hpâ€� is not a measure of energy: Horsepower is power (work per time), not energy. A 1 hp motor running for 1 hour uses 0.7457 kWh of energy (if 100% efficient).

Real-World Context

To give you a feel for what 745.7 W means:

• A typical household microwave oven uses about 1,000 W — about 1.34 hp.
• A small window air conditioner draws about 1,200 W — about 1.6 hp.
• A healthy adult cycling vigorously can sustain about 200–300 W for an hour — about 0.3–0.4 hp.
• A compact car engine might produce 100–200 hp (74.6–149.1 kW).

So one horsepower is roughly the power of a strong person doing hard physical work continuously, or about 10–12 people pedaling stationary bikes.

Why This Conversion Matters

If you are sizing a generator, comparing an electric motor to a gas engine, or reading specifications from different countries, you need to convert between hp and watts or kilowatts. For example, a 5 hp electric motor is about 3.73 kW. If you are buying a generator, you need to know the running watts and starting watts, which are often given in watts or kW, not hp.

In many countries, electrical devices are rated in watts, while engines are rated in horsepower. Understanding the conversion lets you compare them directly.

Frequently Asked Questions

Is 1 hp equal to 746 watts exactly?

Not exactly. 1 mechanical horsepower is 745.69987158227022 W. The value 746 W is a rounded approximation used in electrical engineering, and it is the exact definition of the “electrical horsepower� (a separate unit). For most purposes, 746 W is close enough.

What is the difference between hp and PS?

PS (Pferdestärke) is the German term for metric horsepower. 1 PS = 735.49875 W, while 1 hp (mechanical) = 745.7 W. So 1 hp is about 1.014 PS. Car manufacturers in Europe often quote PS, while the US uses hp.

How many watts is a 1 hp electric motor?

A 1 hp electric motor has a mechanical output of about 745.7 W. However, it draws more electrical power from the wall because of inefficiencies — typically 850–1,000 W depending on the motor’s efficiency rating.

Why is horsepower still used if we have watts?

Tradition and marketing. The automotive industry in the US and UK still uses hp because consumers are familiar with it. Watts and kilowatts are the SI units and are used in most of the world, especially for electrical devices.

How do I convert kW to hp?

Divide the power in kilowatts by 0.7457 to get mechanical horsepower. For example, 1 kW ÷ 0.7457 = 1.341 hp. To convert hp to kW, multiply hp by 0.7457.

Does 1 hp equal 1 horse?

No. James Watt’s definition was based on a typical draft horse, but real horses can briefly produce much more (up to 14 hp in short bursts) and sustain only about 0.7–1 hp for a full workday. The unit is a useful standard, not a biological measurement.

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