Horsepower and torque are two views of the same thing. Torque is the twisting force an engine puts on its crankshaft; horsepower is how quickly that force can be delivered, which also depends on how fast the crankshaft spins. If you know one and the engine speed, you can always find the other. This calculator turns horsepower (or kilowatts) at a given rpm into torque in pound-feet and newton-metres.
How to use the horsepower to torque calculator
- Enter the power in horsepower or kilowatts (use the menu).
- Enter the engine speed in rpm at which that power is produced. Peak horsepower is usually quoted at a specific rpm, such as 300 hp @ 6,000 rpm.
- Read the torque in lb-ft and N·m.
To go in the other direction, use the torque to horsepower calculator.
Horsepower to torque formula
Torque (N·m) = power (W) × 60 ÷ (2π × rpm) = lb-ft × 1.3558
The constant 5,252 is not arbitrary. James Watt’s unit defines one horsepower as 33,000 foot-pounds of work per minute. One revolution carries a torque through an angle of 2π radians, so the work per minute at N rpm is 2π × N × T. Setting 2π × N × T = 33,000 × hp gives T = hp × 33,000 ÷ (2π × N) = hp × 5,252.1 ÷ N.
Worked example
A sports car is rated at 400 hp at 6,000 rpm.
- Torque = 400 × 5,252.1 ÷ 6,000 = 350.1 lb-ft.
- In newton-metres: 350.1 × 1.3558 = 474.7 N·m.
The same engine making 400 hp at 4,000 rpm would have to produce 525.2 lb-ft; the engine speed at which the power is made matters as much as the figure itself.
Torque for 300 hp at different engine speeds
Computed from the formula. The lower the rpm, the more torque it takes to make the same power.
| Engine speed (rpm) | Torque (lb-ft) for 300 hp | Torque (N·m) |
|---|---|---|
| 2,000 | 788 | 1068 |
| 3,000 | 525 | 712 |
| 4,000 | 394 | 534 |
| 5,252 | 300 | 407 |
| 6,000 | 263 | 356 |
| 7,000 | 225 | 305 |
What the number tells you
Because power is torque times speed, a high-revving engine can make a lot of horsepower from modest torque, while a diesel truck engine makes much of its power at low rpm from large torque. Neither is better in itself: transmission gearing multiplies torque and divides speed, so the power reaching the wheels is the same apart from losses. What the two figures predict differently is how the car feels — torque at low rpm gives easy, relaxed pulling, while high horsepower at high rpm gives top-end performance.
The quoted peak horsepower and peak torque happen at different engine speeds, so you cannot apply this formula to the two peak figures together unless they are at the same rpm. The correct use is for power and torque at the same rpm, which you can read from a dynamometer chart. To see how gearing turns engine torque into wheel force and speed, continue to the gear ratio calculator.
Sources
The horsepower definition (33,000 ft·lbf/min = 550 ft·lbf/s) is the standard mechanical horsepower; the metric conversion factor 1 lb-ft = 1.3558179 N·m is exact from the definitions of the pound-force and the foot (NIST SP 811).
Frequently asked questions
How do I convert horsepower to torque?
Torque in pound-feet = horsepower × 5,252 ÷ rpm. A 300 hp engine making that power at 6,000 rpm produces 300 × 5,252 ÷ 6,000 = 262.6 lb-ft.
Where does the number 5,252 come from?
One horsepower is defined as 33,000 foot-pounds per minute. Power is torque times angular speed (2π per revolution), so torque = 33,000 × hp ÷ (2π × rpm), and 33,000 ÷ 2π = 5,252.1.
Why do torque and horsepower curves cross at 5,252 rpm?
Because at 5,252 rpm the conversion factor equals 1, torque in lb-ft and horsepower are numerically the same. On a dyno chart plotted with the same scale the two curves always intersect there.
How do I get newton-metres?
Multiply pound-feet by 1.3558. The calculator also converts kW directly using T = P ÷ ω.
Is this torque at the wheels or the crank?
It is torque at whatever point the horsepower was measured: crank torque for engine horsepower, wheel torque for wheel horsepower measured on a dyno at that wheel speed.