Horsepower Calculator
Horsepower from torque and RPM, or estimated from a trap speed or quarter-mile time.
What do you know?
This converts between horsepower, torque and engine speed, and between horsepower and kilowatts.
It shows why the two curves always cross at 5,252 rpm.
Horsepower and torque
Horsepower is not a separate property from torque. It is torque multiplied by engine speed, scaled by a constant: HP = torque × RPM ÷ 5,252.
Torque is twisting force, and horsepower is the rate at which that force does work. The same 300 lb-ft produces 286 hp at 5,000 rpm and only 171 hp at 3,000 rpm, because the engine is doing the same work fewer times a minute.
The 5,252 is not arbitrary. James Watt defined a horsepower as 33,000 foot-pounds per minute, and converting from rotation to linear motion divides by 2π. 33,000 ÷ 2π = 5,252. That is also why horsepower and torque curves on a dyno chart always cross at exactly 5,252 rpm — at that speed the formula makes them numerically equal.
Below 5,252 rpm, torque reads higher than horsepower. Above it, horsepower reads higher. Every dyno chart shows this.
What to enter
- Torque
- In pound-feet (lb-ft) or newton-metres (Nm). 1 lb-ft is about 1.356 Nm.
- Engine speed
- In revolutions per minute. Horsepower is directly proportional to it at a given torque.
- Horsepower
- To work backwards to torque, or to convert to kilowatts.
Units and conversions
- 1 horsepower (mechanical)
- 745.7 watts, or 33,000 foot-pounds per minute.
- 1 kilowatt
- About 1.341 hp. So 200 hp is 149.1 kW.
- Metric horsepower (PS)
- About 735.5 W, slightly less than mechanical hp. European figures often use it.
- 1 lb-ft
- 1.356 Nm. Note that lb-ft is torque; ft-lb is usually energy, though the two get used interchangeably.
- Brake vs wheel horsepower
- Brake hp is measured at the crank; wheel hp at the wheels, after drivetrain losses of roughly 10-20%.
What this assumes
The 5,252 constant applies to imperial units: pound-feet and rpm. Metric calculations use kW and Nm with a different constant.
Manufacturer figures are usually brake horsepower at the crank. A chassis dyno reads lower because of drivetrain losses.
How to calculate horsepower
One formula, rearranged whichever way you need it.
- 5,252
- 33,000 ÷ 2π, from Watt's original definition
- torque
- In pound-feet for this form of the equation
Get torque and engine speed. Both at the same operating point. Peak torque and peak power usually occur at different rpm.
Multiply them together. 300 lb-ft × 5,000 rpm = 1,500,000.
Divide by 5,252. 1,500,000 ÷ 5,252 = 286 hp.
Convert to kilowatts if needed. Multiply hp by 0.7457. 286 hp is 213 kW.
See a worked example: why rpm matters as much as torque
- Torque
- 300 lb-ft
- Engine speed
- 3,000 rpm, then 5,000
At 3,000 rpm: (300 × 3,000) ÷ 5,252 = 171 hp.
At 5,000 rpm: (300 × 5,000) ÷ 5,252 = 286 hp.
Same twisting force, 67% more power, purely from spinning faster.
This is why a diesel with huge torque at low rpm can make less horsepower than a smaller petrol engine that revs high.
171 hp and 286 hp from identical torque
Frequently asked questions
- What is the difference between horsepower and torque?
Torque is twisting force. Horsepower is the rate at which that force does work, so it accounts for how fast the engine is turning.
They are not independent. HP = torque × RPM ÷ 5,252, so horsepower is derived from torque rather than being a separate quantity.
- Why 5,252?
It comes from Watt's definition of a horsepower as 33,000 foot-pounds per minute, and the conversion from rotational to linear motion, which divides by 2π.
33,000 ÷ 2π = 5,252.1. It is a unit-conversion artefact, not a physical constant.
- Why do power and torque curves always cross at 5,252 rpm?
Because at exactly 5,252 rpm the formula reduces to HP = torque. The RPM term and the constant cancel out.
So on any dyno chart in imperial units the two lines meet there. If a chart shows them crossing anywhere else, it is using different units or is mislabelled.
- How do I convert horsepower to kilowatts?
Multiply by 0.7457, since one mechanical horsepower is 745.7 watts. So 200 hp is 149.1 kW.
Going the other way, multiply kW by 1.341. Watch for metric horsepower (PS), used in some European figures, which is about 735.5 W and gives slightly different numbers.
- What is the difference between brake and wheel horsepower?
Brake horsepower is measured at the crankshaft, which is what manufacturers quote. Wheel horsepower is measured at the wheels on a chassis dyno.
Drivetrain losses of roughly 10-20% separate them, more for all-wheel drive. A car rated at 300 bhp typically reads 240-270 at the wheels.
- Which matters more for acceleration?
Horsepower, because acceleration depends on power available across the rev range and through the gears, not on peak torque at one engine speed.
Torque matters for how the car feels, particularly in normal driving. High torque low down makes a car responsive without needing to rev, which is why diesels feel strong despite modest power figures.
Problems people actually run into
Treating torque and horsepower as independent specs
They are two views of the same measurement. Once you know torque at a given rpm, horsepower is determined; there is no separate quantity to compare.
The useful comparison is the shape of the curves: where peak torque arrives, how flat it is, and how far the power holds before falling away.
Comparing brake horsepower against wheel horsepower
A manufacturer's 300 bhp and a dyno's 260 whp can be the same car. The difference is drivetrain loss, not a discrepancy.
Compare like with like: crank figures against crank figures, or dyno figures from the same type of dyno. Cross-comparing produces conclusions that are simply wrong.
Results are estimates for general information only and are not professional financial, medical, or legal advice. Read our full disclaimer.
Last updated: September 4, 2026
