Horsepower to kW Conversion Formula & Calculator

This calculator converts horsepower (hp) to kilowatts (kW) instantly. Enter the horsepower value, and you get the equivalent power in kilowatts, along with the reverse conversion (kW to hp) for convenience. The formula is simple: 1 horsepower equals 0.7457 kilowatts.

Formula

The conversion between horsepower and kilowatts is a fixed linear relationship:

kW = hp × 0.7457

Where:

• kW = power in kilowatts
• hp = power in mechanical horsepower (the most common type)
• 0.7457 = exact conversion factor (1 hp = 745.7 W)

For the reverse: hp = kW ÷ 0.7457 (or multiply by 1.341).

Worked Example

Using the default value of 100 hp:

1. Start with the formula: kW = hp × 0.7457
2. Plug in 100 hp: kW = 100 × 0.7457
3. Multiply: kW = 74.57

So 100 hp equals 74.57 kW. The calculator shows this rounded to two decimals. The reverse output (74.57 kW ÷ 0.7457) gives 100 hp, confirming the round-trip.

Why 0.7457? The Origin of Horsepower

The term “horsepower� was coined by James Watt in the 18th century to compare the output of steam engines with draft horses. He defined one horsepower as the power needed to lift 33,000 pounds one foot in one minute — that works out to 745.7 watts in modern units. The metric system later adopted the watt as the standard unit of power, and the conversion factor became fixed. Today, the international standard (SI) uses the watt, but horsepower persists in automotive, marine, and industrial contexts, especially in the United States and the UK.

Different Types of Horsepower

Not all horsepower is the same. The most common is mechanical horsepower (hp) used for car engines, which uses the 0.7457 factor. However, there are others:

• Metric horsepower (PS or cv) – used in Europe, equals 735.5 W, so 1 PS = 0.7355 kW.
• Electrical horsepower – used for electric motors, equals exactly 746 W, so 1 hp = 0.746 kW.
• Boiler horsepower – used for steam boilers, equals about 9.81 kW, but this is rare in general use.

When converting, always check which type you’re dealing with. For car engines, mechanical hp is standard. For electric motors, electrical hp might be used. The difference is small (0.3%) but can matter in precise engineering.

How to Read the Result

The result in kilowatts tells you the actual power output in SI units. For example, a 150 hp car engine produces about 112 kW. This is useful when comparing vehicles from different countries — a European car might list power in kW, while a US car lists hp. The conversion lets you compare directly. Also, when calculating energy consumption or electrical load, kW is the standard unit, so converting from hp helps size generators, batteries, or wiring.

Common Mistakes and Misconceptions

• Using the wrong hp type – Mixing up mechanical and metric hp changes the result by about 1.4%. Always confirm which type you have.
• Rounding too early – If you round 0.7457 to 0.75, a 200 hp engine gives 150 kW instead of 149.14 kW — an error of 0.6%.
• Confusing kW with kWh – kW is power (rate of energy use), while kWh is energy (amount). A 100 kW motor running for 1 hour consumes 100 kWh.
• Forgetting the reverse – When converting kW to hp, divide by 0.7457, not multiply. A common error is multiplying, which gives a huge number.

When to Use This Conversion

Use this conversion whenever you need to compare power ratings across different systems:

• Comparing a car’s horsepower to an electric motor’s kilowatt rating.
• Calculating electrical load for a generator or circuit when you know the mechanical power of a device.
• Reading international vehicle specs – many countries list power in kW.
• Engineering calculations where SI units are required.

For example, if you have a 250 hp boat engine and want to know its electrical equivalent for a generator, the answer is 186.4 kW. That tells you the generator must supply at least that much power to run the engine’s electrical systems (though in practice, you’d add a safety margin).

Limits of the Formula

The conversion is exact for mechanical horsepower. However, the actual power output of an engine can vary due to temperature, altitude, fuel quality, and measurement standards (SAE vs DIN). The formula converts the rated number, not the real-world performance. Also, for electric motors, the input electrical power (kW) is not the same as output mechanical power (hp) because of efficiency losses — a motor might draw 10 kW but only deliver 9 kW of mechanical power. This conversion only translates units, not efficiency.

Frequently Asked Questions

How many kW is 1 hp?

Exactly 0.7457 kW for mechanical horsepower. For metric horsepower, it’s 0.7355 kW. For electrical horsepower, it’s 0.746 kW. The difference is small, but for precise work, use the correct factor.

Why do car engines use horsepower instead of kW?

It’s a historical convention. Horsepower was established in the 18th century and became deeply embedded in the automotive industry, especially in the US and UK. Most of the world officially uses kilowatts, but horsepower remains in marketing and everyday conversation because people have a feel for it.

Is 1 hp equal to 1 kW?

No. 1 hp is about 0.746 kW, so 1 kW is about 1.34 hp. They are close but not equal. A 100 kW motor is roughly 134 hp.

How do I convert kW to horsepower?

Divide the kW value by 0.7457 (or multiply by 1.341). For example, 150 kW ÷ 0.7457 = 201 hp. The calculator above also shows this in the reverse output.

What is the difference between hp and bhp?

Bhp (brake horsepower) is the power measured at the engine’s crankshaft without losses from the gearbox, alternator, or other accessories. Hp often refers to the same thing in casual use, but technically hp can be measured at the wheels (whp) or at the crank. The conversion factor is the same for both — 1 bhp = 0.7457 kW.

Does the conversion work for electric motors?

Yes, but be careful: the hp rating of an electric motor is typically the mechanical output power, while the kW rating might be the electrical input power. To convert between them, you need to know the motor’s efficiency. The unit conversion itself is the same, but the actual power relationship includes efficiency losses.

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in hp | Horsepower | hp | 100 | 0
out kw | Kilowatts | kW | hp * 0.7457 | 2
out hp_rev | Reverse (kW to hp) | hp | kw / 0.7457 | 2