Kilowatts to mechanical horsepower

What the units mean

Convert kilowatts (kW) to mechanical horsepower (hp) instantly in your browser. See the formula, a worked example and limits of the result.

Power is the rate at which energy is transferred. A watt means one joule per second; a kilowatt means one thousand watts. Vehicle, motor and equipment specifications sometimes quote mechanical horsepower, a legacy unit that can be compared with SI power once its definition is clear.

This page converts one named unit into another within the same physical or digital quantity. The input stays in the browser. The result is a change of representation: it does not estimate an unmeasured property, correct a label, or supply missing information about the object being measured. Identify the original unit before typing a number, especially when a symbol could have more than one informal meaning.

How to calculate

hp = kW × 1.34102208960. Horsepower means mechanical hp (550 ft·lbf/s), not metric horsepower.

Use the displayed relationship with the entered value in the source unit. For an ordinary linear conversion, multiply by the ratio of the source unit to the destination unit. The reverse direction divides by that same ratio. Fuel economy is the exception here: it uses a reciprocal, so the number appears in the denominator. The calculator carries the defined constants through the calculation before shortening the displayed decimal.

As a worked example, enter 100 kW. The output is 134.10220896 hp. Put the unit beside both numbers when copying them into a document or spreadsheet. A number without its unit does not reveal the measurement scale, and switching the order of the units changes the operation. The example is illustrative; use the value from your own measurement for a real comparison.

When this conversion is useful

Engine specifications often give kW and hp, but the quoted rating can refer to different test standards or operating speeds. This page uses mechanical horsepower, not metric PS or CV. A horsepower conversion changes only the unit of a given power figure; it does not predict wheel power, acceleration, torque or fuel economy.

Start with a figure explicitly reported in kilowatts (kW) and read the answer in mechanical horsepower (hp). A smaller or larger output number alone says nothing about whether the measured quantity has changed. If the original source gives a rounded value, the calculation cannot recover digits that were never measured. For a critical limit, compare using the unrounded numerical result and round only the final presentation.

Precision and common mistakes

The horsepower unit here is mechanical horsepower based on 550 foot-pounds force per second, equivalent to about 745.6998716 W. Metric horsepower and electrical horsepower use different factors. A nameplate rating may also refer to input, shaft output, peak or continuous power. Converting the unit cannot reconcile those different measurement conditions.

Conversion factors can be defined exactly even when the decimal displayed on the page has been shortened. Values involving π are approximated by computer arithmetic; a stated measurement may have much greater uncertainty than that arithmetic. Carry the source unit and enough significant figures through intermediate steps. If you need a certified measurement, calibration or commercial settlement, use the applicable standard and the original instrument record.

Questions about the result

Why can a reverse conversion return a slightly different final digit? The visible result is rounded to make it readable; reversing that shortened number starts from a different input. Why does a plausible figure sometimes disagree with a product label? The label may use another convention, a different reference condition or fewer significant figures. Confirm the exact unit symbol and the measurement definition before deciding that either number is wrong.