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Horsepower Calculator

Calculate horsepower from torque and RPM, or convert between horsepower, watts, and kilowatts.

By Christopher FloiedPublished Updated

Range: 1 – 10,000

Torque in pound-feet.

Range: 100 – 20,000

Results

Horsepower

238 hp

Kilowatts

177.5 kW

Watts

177480 W

How to Use This Calculator

1

Enter your input values

Fill in all required input fields for the Horsepower Calculator. Follow the units and input format printed next to each field. Where a unit selector is available, choose the units that match your data.

2

Review your inputs

Double-check that all values are correct and match the units or format shown for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.

3

Read the results

The Horsepower Calculator computes the output in your browser and displays the results, with units clearly labeled, as soon as they are ready — no data sent to a server.

4

Explore parameter sensitivity

Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.

When to Use This Calculator

  • •Use the Horsepower Calculator when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
  • •Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
  • •Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
  • •Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.

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About Horsepower Calculator

Horsepower is the most commonly referenced measure of engine output, used for everything from car specs to lawn mower ratings. The Horsepower Calculator computes power from torque and RPM using the classic mechanical relationship, and also converts to metric units (kilowatts and watts). Understanding the interplay between torque and RPM is essential for evaluating vehicle performance: a diesel truck may produce high torque at low RPM, while a sports car engine generates peak power at high RPM. The constant 5252 appears because one horsepower was defined by James Watt as 33,000 foot-pounds of work per minute, and 33,000 divided by 2 x pi equals 5252.

The Math Behind It

Power is the rate of doing work. James Watt defined one horsepower as the ability to lift 33,000 pounds one foot in one minute, based on his observations of draft horses. For rotating machinery, power equals torque times angular velocity. Since torque is measured in pound-feet and angular velocity in radians per minute (RPM x 2pi), the formula becomes HP = Torque x RPM x 2pi / 33000, which simplifies to HP = Torque x RPM / 5252. At exactly 5252 RPM, torque in lb-ft and horsepower are numerically equal, which is why torque and horsepower curves on a dyno chart always cross at that point. Metric horsepower (PS, from Pferdestarke) equals 735.5 watts, slightly less than mechanical horsepower (745.7 watts). Electric motors are rated in kilowatts; 1 hp equals approximately 0.746 kW. Electric motors deliver peak torque at 0 RPM, which is why electric vehicles feel so quick off the line compared to internal combustion engines that must build RPM to reach peak power.

Formula Reference

Horsepower Formula

HP = Torque(lb-ft) x RPM / 5252

Variables: Torque in pound-feet; RPM = engine revolutions per minute; 5252 = 33000/(2xPI)

Worked Examples

Example 1: 250 lb-ft at 5000 RPM

An engine produces 250 lb-ft of torque at 5000 RPM.

Step 1:HP = 250 x 5000 / 5252 = 238.0 hp
Step 2:kW = 238.0 x 0.7457 = 177.5 kW

The engine produces 238 horsepower (177.5 kW) at this RPM.

Common Mistakes & Tips

  • !Confusing torque and horsepower; torque is a force, horsepower is the rate of applying that force.
  • !Using the formula at a single RPM point; peak HP and peak torque occur at different RPMs.
  • !Mixing mechanical HP and metric PS; they differ by about 1.4%.

Related Concepts

Cycling Wattage

Power output measurement for human-powered transport.

Frequently Asked Questions

Why do torque and horsepower always cross at 5252 RPM?

Because HP = Torque x RPM / 5252. At 5252 RPM, HP = Torque x 1, so they are numerically equal. Below that RPM, torque is higher; above it, horsepower is higher.

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