How to use it
- Choose What do you want to work out?: power from a torque and a speed, torque from a power and a speed, a table for a flat torque, or the peak power of a torque curve.
- Enter the Torque and the Engine speed, rpm. For torque from power, enter the Power with its Power unit and the Engine speed, rpm.
- For a table, enter the Lowest engine speed, rpm, the Highest engine speed, rpm and the Step, rpm, or paste the Torque curve: one line for each point.
- Read Power, kW, Power, PS (metric horsepower) and Power, hp (mechanical horsepower), or Torque, N·m and Torque, lb·ft. For a table, read Highest power of the table and the rows of Power across the rev range.
How power and torque are linked
Power is the rate at which work is done. The power of a turning engine is its torque times its angular speed. An engine turning at rpm has an angular speed of 2π × rpm ÷ 60 radians per second, so at 1,000 rpm one newton-metre of torque makes 104.7 watts.
Power (W) = torque (N·m) × 2π × rpm ÷ 60
Power (kW) = torque (N·m) × rpm ÷ 9,549.3
Torque (N·m) = power (W) × 60 ÷ (2π × rpm)
PS = kW × 1,000 ÷ 735.49875; hp = kW × 1,000 ÷ 745.69987
1 lb·ft = 1.35582 N·mHorsepower: PS, hp and kW
A metric horsepower (PS) is 735.49875 watts. The mechanical horsepower (hp) of the US and UK is 745.69987 watts. So one PS is 98.6 per cent of one hp, and a kilowatt is about 1.36 PS or 1.34 hp.
- The US formula hp = lb·ft × rpm ÷ 5252 gives the same hp. The constant 5252 is 33,000 ÷ (2π), rounded.
- A figure in kW is the same power whatever unit the maker uses; only the name changes.
What this calculator does not include
- Losses in the gearbox and the drive: the power here is the power of the engine, not the power at the wheels.
- Corrections to standard air, which makers apply to their published figures.
- The shape of a torque curve between the points you give: the highest power is only as exact as the points.
Worked example: 300 N·m at 5,000 rpm
Power: 300 × 2π × 5,000 ÷ 60 = 157,080 W, which is 157.1 kW. In metric horsepower that is 157,080 ÷ 735.49875 = 213.6 PS, and in mechanical horsepower 157,080 ÷ 745.69987 = 210.6 hp.
The other way round: 150 kW at 6,000 rpm needs a torque of 150,000 × 60 ÷ (2π × 6,000) = 238.7 N·m, which is 176.1 lb·ft.
| Result | |
|---|---|
| Power from 300 N·m at 5,000 rpm | 157.1 kW (213.6 PS, 210.6 hp) |
| Torque from 150 kW at 6,000 rpm | 238.7 N·m (176.1 lb·ft) |
Frequently asked questions
What is the difference between torque and power?
Torque is a turning force, measured in N·m or lb·ft. Power is how fast that work is done, measured in kW, PS or hp. Power equals torque times speed, so an engine with a lot of torque at low rpm still makes little power there.
How do I convert kW to hp?
Divide the kilowatts by 0.7457 to get mechanical horsepower (hp), or by 0.7355 to get metric horsepower (PS). For example 100 kW is 134.1 hp or 136.0 PS. The calculator does the sum for you.
What is the difference between PS and hp?
PS is 735.49875 watts and hp is 745.69987 watts, so one PS is about 98.6 per cent of one hp. Check which unit a maker's figure uses before you compare two engines.
Why is the highest power not at the speed of the highest torque?
Power is torque times speed. Speed keeps rising while torque falls, so the product peaks where the rise in speed outweighs the fall in torque. That point is often at a higher rpm than the peak torque.
Why does the power in a brochure differ from this result?
Published power depends on the test standard and is corrected to standard air. The torque you enter is the value measured at one speed, so the result is only as exact as that figure.
Does the calculator keep the numbers I type?
No. The calculation runs in your browser, and nothing you type is sent to a server or saved for later.
Sources
- Wikipedia: Torque (power = torque × 2π × rpm, with rpm)
- Wikipedia: Horsepower (metric 735.49875 W, mechanical 745.69987 W, and the 5252 constant)
Figures and text last checked on Tuesday, November 10, 2026.