How Much Is One Horsepower in Watts?

One horsepower equals exactly 745.69987158227022 watts (about 746 W) in the mechanical system, and 735.49875 watts in the metric system. This calculator converts horsepower to watts using either definition, so you can see the difference for yourself.

Formula

The conversion is straightforward: Watts = Horsepower × 745.69987158227022 (mechanical) or Watts = Horsepower × 735.49875 (metric).

• Horsepower (hp) – the power input you provide, in horsepower.
• Watts (W) – the resulting power in the SI unit.
• Kilowatts (kW) – watts divided by 1,000, commonly used for electric motors and appliances.

The mechanical horsepower (also called imperial horsepower) is the one used for car engines in the US and UK. The metric horsepower (PS or cv) is used in most of Europe and Asia. Both are close but not identical.

Worked Example

Using the default values: 1 horsepower, mechanical system.

1. Start with the formula: Watts = 1 × 745.69987158227022
2. Multiply: 1 × 745.69987158227022 = 745.69987158227022 W
3. Convert to kilowatts: 745.69987158227022 ÷ 1000 = 0.746 kW

The calculator shows 745.70 W and 0.746 kW for 1 mechanical horsepower. If you switch to metric, you get 735.50 W and 0.736 kW.

Why Are There Different Horsepower Definitions?

James Watt defined the original unit in the late 18th century to compare steam engines with draft horses. He measured that a horse could lift 33,000 pound-feet per minute, which equals 745.7 watts. That became the mechanical horsepower.

Later, continental Europe adopted a slightly different value based on the metric system: 75 kilogram-force meters per second, which equals 735.49875 watts. This is called metric horsepower (PS, cv, or ch).

There are also other variants you might encounter:

• Electric horsepower – exactly 746 watts, used for electric motors in some contexts.
• Boiler horsepower – about 9,809.5 watts, used for steam boilers.
• Hydraulic horsepower – flow rate × pressure, often used in pump calculations.

For most everyday purposes, the mechanical value (745.7 W) is what people mean when they say “horsepower” without a qualifier.

How to Read the Result

The watt is the SI unit of power, and it tells you how much energy is used or produced per second. One watt is one joule per second. So 745.7 watts means the engine can do 745.7 joules of work every second.

In practical terms, a typical household light bulb uses 60–100 watts, a microwave uses about 1,000 watts, and a small car engine produces around 75,000–150,000 watts (100–200 hp).

When comparing engines, remember that the horsepower number on a spec sheet is the maximum output at a specific RPM. The actual power you use while driving varies constantly.

Common Mistakes and Misconceptions

One frequent error is mixing up mechanical and metric horsepower. If you convert a European car’s PS rating using the mechanical factor, you’ll be off by about 1.4%. That’s small but can matter in calculations.

Another mistake is confusing horsepower with torque. Torque is a twisting force (measured in pound-feet or newton-meters), while horsepower is the rate at which work is done. They are related: Horsepower = Torque × RPM / 5252 (in imperial units). At 5,252 RPM, torque and horsepower are numerically equal.

Also, don’t forget that the watt is a unit of power, not energy. A 745.7-watt engine running for one hour consumes 745.7 watt-hours of energy (about 0.746 kWh). Power is instantaneous; energy is accumulated over time.

When to Use Mechanical vs. Metric Horsepower

Use the mechanical value (745.7 W) when you are dealing with:

• US or UK car specifications
• Imperial unit calculations
• Classic steam engine references

Use the metric value (735.5 W) when you are dealing with:

• European or Asian car specs (PS, cv, ch)
• Metric unit calculations
• Most international engineering standards (though many now use kilowatts directly)

If you are unsure, check the unit label: “hp” usually means mechanical, “PS” or “cv” means metric, and “kW” is always kilowatts.

Why This Conversion Matters

Knowing the watt equivalent helps you compare engines with electric motors, which are rated in watts or kilowatts. For example, a 100 hp car engine has about 74.6 kW of mechanical output. An electric motor with the same power rating would produce the same amount of work per second.

It also helps with energy cost estimates. If you know a machine’s horsepower, you can estimate its electrical consumption (though real motors are not 100% efficient). A 10 hp motor, for instance, draws about 7.46 kW of electrical power under full load, plus losses.

Finally, it gives you a sense of scale. A human can sustain about 0.1 horsepower (75 W) for a while, a horse can do about 1 horsepower, and a small car has 100–200 horsepower. The unit is old but still useful for quick comparisons.

Frequently Asked Questions

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

Not exactly. James Watt deliberately overestimated the power of a horse so that his steam engines would sell well. A healthy horse can produce about 0.7 to 1.0 horsepower sustained, but can briefly produce much more. The unit is a fixed definition, not a biological measurement.

What is the difference between bhp and hp?

Bhp stands for brake horsepower, which is the power measured at the engine’s output shaft (crankshaft) before losses from the transmission. “Hp” often refers to the same thing in casual use, but sometimes it means power at the wheels (whp). Bhp is always higher than whp because of drivetrain losses.

How many watts is 1 kilowatt?

1 kilowatt = 1,000 watts. So 1 mechanical horsepower = 0.7457 kW, and 1 metric horsepower = 0.7355 kW. Electric car motors are often rated in kilowatts; a 150 kW motor is about 201 mechanical horsepower.

Why do some countries use PS instead of hp?

PS stands for Pferdestärke, German for “horse strength.” It is the metric horsepower, defined as 735.49875 watts. It was adopted in Europe to use round metric numbers. The difference between PS and hp is about 1.4%, so for most practical purposes they are interchangeable.

How do I convert horsepower to watts for a specific engine?

Find the horsepower rating (check if it’s mechanical or metric), then multiply by 745.7 (mechanical) or 735.5 (metric). For example, a 200 hp engine produces 200 × 745.7 = 149,140 W (149.14 kW). Use the calculator above to avoid arithmetic errors.

What is the difference between watts and watt-hours?

Watts measure power (rate of energy use), while watt-hours measure energy (total amount). A 745.7 W engine running for 2 hours uses 1,491.4 watt-hours (1.4914 kWh). Your electricity bill charges you for kilowatt-hours, not kilowatts.

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in hp | Horsepower | hp | 1 | 0
sel type | System | Mechanical=745.69987158227022, Metric=735.49875 | 2
out watts | Watts | W | hp * type | 2
out kilowatts | Kilowatts | kW | (hp * type) / 1000 | 3