Horsepower Calculator

Convert torque and RPM into horsepower and kilowatts.

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Torque (lb-ft)

RPM

Result

Enter values to calculate.

Summary

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Detail

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Convert an engine's torque and RPM into horsepower and kilowatts using the standard automotive horsepower formula.

How It Works

How Horsepower Calculator Works

Horsepower is calculated as (torque in lb-ft × RPM) ÷ 5252. The constant 5252 comes from the mechanical definition of horsepower itself (33,000 ft-lb per minute) combined with the conversion between RPM and radians per minute — it's also the exact RPM at which a torque and horsepower curve, plotted on the same graph, always cross.

The result is also converted to kilowatts by multiplying by 0.7457, the standard conversion factor between horsepower and kilowatts, since kilowatts are the more common power unit outside the US.

Worked Example

See It In Action

An engine producing 300 lb-ft of torque at 4,000 RPM is putting out about 228.5 horsepower — roughly 170.4 kW.

Real-World Use Cases

Who Uses Horsepower Calculator and Why

Converting a dyno sheet's torque and RPM readings into a horsepower figure to compare against a manufacturer's advertised rating.
Understanding where in the RPM range an engine is making its peak power, given a torque curve read off at several RPM points.
Converting an American horsepower figure into kilowatts for comparison against a European or metric spec sheet.
Working out the horsepower implied by a torque figure and shift point when tuning or evaluating engine modifications.

Common Mistakes

Mistakes to Avoid

Plugging in torque from a different unit system (like Newton-meters) without converting to pound-feet first — the 5,252 constant in this formula only holds for pound-feet and RPM.
Assuming peak torque RPM and peak horsepower RPM are the same value — they usually aren't, and entering the torque figure at the wrong RPM point will misstate peak horsepower.
Treating a single torque-and-RPM pair as the engine's entire power curve — this calculator gives horsepower at one specific RPM, not the shape of the curve across the rev range.

Pro Tips

Tips for Best Results

Run the calculation at several RPM points along a torque curve, not just one, if you want to see how horsepower rises and falls across the rev range rather than at a single instant.
Remember the 5,252 RPM crossover point is a mathematical property of the formula itself, not something specific to any one engine — it will show up on every torque-versus-horsepower chart, regardless of the vehicle.

Troubleshooting

Fixing Common Problems

My horsepower figure doesn't match what the manufacturer advertises. — Factory ratings are usually measured at the engine's actual peak-power RPM under controlled dyno conditions — if you entered torque and RPM from a different point in the curve, or from a wheel dyno rather than an engine dyno, some difference is expected.

My torque and horsepower numbers came out equal. — That's expected only at 5,252 RPM specifically — if you got equal numbers at a different RPM, double-check the RPM value entered, since it's easy to mistype an extra digit.

Glossary

Terms Explained

Torque: A twisting force, measured here in pound-feet, that reflects an engine's ability to do work rather than how fast it can spin.

5,252 constant: The fixed number that torque times RPM is divided by to yield horsepower, a consequence of the mechanical definition of one horsepower combined with the units used for torque and rotational speed.

FAQ

Frequently Asked Questions

Why do torque and horsepower curves always cross at 5252 RPM?

It's a direct mathematical consequence of the horsepower formula itself — at exactly 5252 RPM, the horsepower value and torque value (in lb-ft) are always numerically equal, regardless of the engine, which is why dyno charts consistently show the two lines crossing at that same point.

Which matters more, horsepower or torque?

Torque is the twisting force an engine produces at a given moment (how strong it feels off the line), while horsepower reflects how quickly that work can be done over time (how it performs at higher RPM) — both matter, and their relative importance depends on the application, like towing versus top-speed performance.

Why does the calculator need both torque and RPM?

Horsepower isn't a directly measured quantity — it's calculated from torque and rotational speed together, since power is the rate at which work (torque) is done over time (RPM).

Will this match a dyno-measured horsepower figure?

This calculates theoretical horsepower directly from torque and RPM. Dyno results can differ slightly due to how and where torque is measured, drivetrain losses, and correction factors for temperature and altitude.