Horsepower to Kilowatts Calculator & Conversion

This calculator converts horsepower (hp) to kilowatts (kW) instantly. You enter the power value in horsepower, select the type (mechanical, metric, electrical, or boiler), and get the equivalent in kilowatts, plus the reverse conversion. The formula is simple: 1 mechanical horsepower equals 0.7457 kilowatts.

Formula

The core formula for converting mechanical horsepower to kilowatts is:

kW = hp × 0.7457

Where:

• kW = power in kilowatts
• hp = power in mechanical horsepower
• 0.7457 = the exact conversion factor (1 hp = 745.7 watts)

For other horsepower definitions, the factor changes:

• Metric horsepower (PS): 1 PS = 0.735499 kW
• Electrical horsepower: 1 hp = 0.746 kW
• Boiler horsepower: 1 hp = 9.8095 kW

Worked Example

Using the default values from the calculator (100 mechanical hp):

1. Start with the formula: kW = hp × 0.7457
2. Plug in 100 hp: kW = 100 × 0.7457
3. Multiply: kW = 74.57
4. Rounded to 3 decimal places: 74.570 kW

To reverse it, take the kW result and divide by 0.7457: 74.57 / 0.7457 = 100.000 hp, as shown in the second output.

Why There Are Different Horsepower Definitions

Horsepower originated with James Watt in the 18th century to compare steam engines to draft horses. He defined 1 hp as 550 foot-pounds per second (about 745.7 watts). However, different industries and countries developed their own standards:

• Mechanical horsepower (hp) – used in the US and UK for automotive and machinery; exactly 745.7 W.
• Metric horsepower (PS or cv) – used in Europe and Asia; defined as 75 kgf·m/s, which equals 735.49875 W.
• Electrical horsepower – used for electric motors; exactly 746 W.
• Boiler horsepower – used for steam boilers; equals the heat needed to evaporate 34.5 lb of water per hour, about 9.81 kW.

When someone says “horsepower� without qualification, they almost always mean mechanical horsepower. But for electric motors, the electrical definition is common. Using the wrong factor can cause errors of up to 1.4% – small but sometimes significant in engineering.

How to Choose the Right Horsepower Type

Select the type based on the context of your power rating:

• If you are converting a car engine’s power (especially from a US or UK spec sheet), use mechanical hp.
• If the rating is from a European or Asian vehicle (often labeled PS or cv), use metric hp.
• If you have an electric motor nameplate, use electrical hp (though many motor ratings are already in kW).
• If you are dealing with a steam boiler, use boiler hp.

When in doubt, check the equipment’s documentation or the label. Many international standards now use kilowatts directly, so you may not need to convert at all.

Common Mistakes and Misconceptions

One frequent error is mixing up metric and mechanical horsepower. For example, a European car rated at 150 PS is 110.3 kW, but if you mistakenly treat it as mechanical hp, you get 111.9 kW – a difference of 1.6 kW that could affect performance calculations.

Another mistake is forgetting that 1 hp = 0.7457 kW, not 0.75 kW. The 0.75 approximation is close (0.6% error) but not exact. For critical engineering, always use the full factor.

Also, remember that horsepower is a unit of power (energy per time), not torque or force. Torque and horsepower are related by RPM, but that is a separate calculation.

When to Use This Conversion

You need this conversion in many practical situations:

• Comparing power outputs of vehicles from different countries (e.g., a US car vs. a European car).
• Specifying electric motor replacements – many motors are rated in kW, but older ones may be in hp.
• Calculating energy costs – electricity is billed per kWh, so knowing the kW rating helps estimate running costs.
• Reading engineering standards that require SI units (kW).

The conversion is purely multiplicative, so it works for any power value, from small motors (fractional hp) to large industrial turbines (thousands of hp).

Limitations and Accuracy

This calculator assumes the input is a steady-state power rating. Real-world power can vary with conditions (temperature, load, RPM), but the conversion factor itself is constant. The result is accurate to the number of decimal places shown (3), which is sufficient for most purposes.

If you need more precision, use the full factor 0.7456998715822702 for mechanical hp. The calculator uses 0.7457, which is accurate to 0.00003%.

Frequently Asked Questions

How many kilowatts is 1 horsepower?

1 mechanical horsepower equals 0.7457 kilowatts. For metric horsepower, it’s 0.735499 kW; for electrical horsepower, 0.746 kW.

Is hp or kW bigger?

A kilowatt is larger than a horsepower. 1 kW equals about 1.341 mechanical horsepower. So 100 kW is roughly 134 hp.

Why do cars use hp in the US but kW in Europe?

The US historically used Imperial units, while most of the world adopted the metric system. However, many countries now list both, and electric vehicles often use kW exclusively.

How do I convert kW to hp?

Divide the kW value by 0.7457 to get mechanical horsepower. For example, 50 kW ÷ 0.7457 = 67.05 hp.

Does the conversion factor change for electric motors?

Yes, electric motors often use the electrical horsepower definition (1 hp = 0.746 kW). But many modern motor nameplates list power in kW directly, so conversion may not be needed.

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in hp | Horsepower (mechanical) | hp | 100 | 0
sel type | Horsepower type | Mechanical=0.7457, Metric=0.735499, Electrical=0.746, Boiler=9.8095
out kw | Kilowatts | kW | hp * type | 3
out hp_rev | Horsepower (from kW) | hp | (hp * type) / 0.7457 | 3