HP to KW Converter

How to convert horsepower to kilowatts

Converting horsepower to kilowatts is a single multiplication. The formula is hp × 0.745699 = kW, which means one horsepower equals 0.745699 kW. Going the other way, one kilowatt equals 1.3410237 hp.

The calculator above applies this automatically as you type, but it is worth knowing the arithmetic if you need to sanity-check a figure or work one out without a device to hand.

Worked examples

7 hp to kW: multiply 7 by 0.745699, which gives 5.219893 kW.

45 hp to kW: multiply 45 by 0.745699, which gives 33.556455 kW.

250 hp to kW: multiply 250 by 0.745699, which gives 186.42475 kW.

HP to KW conversion table

The values below are calculated with the same function as the converter above, so they agree to the digit. Use it as a quick reference when you need a rough figure without typing anything.

What is a horsepower?

Mechanical horsepower is defined as 33,000 foot-pounds of work per minute, which equals about 745.7 watts. Metric horsepower, used in much of Europe and abbreviated PS or CV, is slightly different at about 735.5 watts.

Where the horsepower came from

James Watt coined the unit in the 1780s to sell steam engines to mill owners who thought in terms of horses. He measured how much work a strong dray horse could sustain and rounded it into a figure buyers could compare against the animals they were replacing.

Where horsepower are used today

Horsepower is how engine output is quoted for cars, motorcycles, boats, and lawn equipment in the US and UK. Manufacturers elsewhere often quote kilowatts or PS, so the same engine can carry three different-looking numbers.

• A small family car is about 120 hp
• A lawnmower engine is 4 to 7 hp
• A sports car can exceed 500 hp

What is a kilowatt?

A kilowatt is one thousand watts, the SI unit of power, meaning one thousand joules of energy transferred per second. A kilowatt-hour, the unit on an electricity bill, is a unit of energy rather than power: one kilowatt sustained for one hour.

Where the kilowatt came from

The watt is named for James Watt, the same engineer who coined horsepower, and was adopted as the SI unit of power in 1960. There is a certain symmetry in the fact that the unit replacing horsepower is named after the man who invented horsepower.

Where kilowatts are used today

Kilowatts state the output of electric motors and EV powertrains, the capacity of solar installations and generators, and the draw of large appliances. EU regulations require vehicle power to be given in kilowatts, often with horsepower alongside.

• An electric kettle draws about 3 kW
• A home solar array is often 4 to 6 kW
• A family car is roughly 90 kW

When you actually need this conversion

horsepower belong to the imperial / us customary system and kilowatts to the metric (si) system, so this conversion turns up whenever information crosses between countries that measure differently.

Accuracy, precision, and rounding

The factor used here (hp × 0.745699 = kW) is the standard accepted value. The results above are shown to about eight significant figures, which is more precision than almost any practical use requires.

The sensible rule is to round the answer to roughly the same precision as the number you started with. If you measured to the nearest horsepower, an answer carrying six decimal places is not more accurate, it just looks more accurate. For most everyday purposes one or two decimal places is plenty.

Common mistakes to avoid

Converting in the wrong direction

Multiplying when you should divide is by far the most common error, and it is easy to miss because the result is still a number in a believable range. A quick check: since one horsepower is 0.745699 kW, a horsepower value should get smaller when converted.

Using a rounded factor for a long calculation

Rounding the conversion factor before multiplying, then repeating that across many values, compounds the error. Convert with the full factor and round only the final answer.

Converting horsepower to kilowatts in a spreadsheet or in code

A one-off answer is what the calculator above is for. When you have a whole column of figures, or you are writing something that has to do the conversion repeatedly, it is worth putting the formula in the tool you are already working in.

Excel and Google Sheets

With your horsepower value in cell A1, put this in B1 and fill it down the column:

=A1 * 0.745699

Excel also ships a built-in CONVERT function that handles many unit pairs directly, but it does not cover every unit and its unit codes are easy to mistype. An explicit formula like the one above is harder to get wrong and shows its working.

Python

def hp_to_kw(value):
    return value * 0.745699

print(hp_to_kw(10))

JavaScript

const hpToKw = (value) => value * 0.745699;

console.log(hpToKw(10));

Store the factor as a named constant rather than typing 0.745699 at each call site. When a figure appears in three places it will eventually be updated in two of them.

The two measurement systems behind this conversion

This conversion sits on the fault line between the two measurement systems still in everyday use. The metric system was designed in one go in the 1790s as a coherent decimal scheme, where every unit relates to the next by a power of ten. The imperial and US customary systems grew instead by accretion over centuries, which is why their relationships are numbers like 12, 16, 5,280, and 43,560 rather than round ones.

Only three countries have not formally adopted the metric system: the United States, Liberia, and Myanmar. In practice the picture is messier than that, since the US uses metric units throughout science, medicine, and the military, while metric countries still buy screens and tires by the inch. That overlap is exactly why conversions like this one stay necessary.

More questions about horsepower and kilowatts

Is the conversion exact or approximate?

The underlying definition is exact, and the factor shown here (0.745699) is that definition expressed to the precision this page displays. For any everyday purpose the result is exact; only at very high precision would you need more digits of the factor.

Why does the answer have so many decimal places?

The converter shows a high-precision result so that it is never the limiting factor in your calculation. It is up to you to round to something sensible. A measurement taken with a tape measure does not become more accurate because the conversion carried six decimals.

Can I convert in the opposite direction on this page?

Yes. The swap button in the calculator reverses the conversion and carries the current result across as the new input, so you do not have to navigate anywhere or retype anything. The second table above also lists the reverse conversion directly.

Does anything get sent to a server?

No. The arithmetic runs in your browser with a few lines of JavaScript. Nothing you type is uploaded, logged, or stored, which also means the converter keeps working if your connection drops after the page has loaded.

Which figure should I use on an official form?

Use whatever precision the form asks for, and if it does not say, match the precision of the original measurement. For height, weight, and similar personal details, one decimal place is almost always sufficient and often more than is wanted.

Related power conversions

If you need to go the other way as a starting point rather than as a swap, the KW to HP converter is the mirror of this page: same factor, same tables, opposite direction. It is the more natural place to start when most of your figures are already in kilowatts.

This is a small category, so the list below reaches into the other measurement families as well:

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• Acres to Square Feet - Convert acres to square feet instantly. Ideal for real estate, land surveying, and property measurements.

For anything not listed here, the full converter directory covers over a hundred pairs across length, weight, temperature, volume, area, speed, pressure, energy, and more.

Quick reference

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