Torque / Power / RPM Calculator
Compute engine or motor power from torque and rotational speed.
Formula
P = T × ω, ω = 2πN / 60
Inputs
- Torque (N·m)
- Engine speed (RPM)
Notes and assumptions
- Shares its formula with Mechanical Engineering's Mechanical Power calculator — one engineering relationship, two entry points.
What it does
Power is torque times rotational speed: P = T × ω, with ω = 2πN / 60.
Where it's used
Engine and motor specifications, dynamometer results and drivetrain sizing.
How to use it
- Enter the torque in N·m.
- Enter the speed in rpm.
- Read the power.
The formula explained
- P
- power, W
- T
- torque, N·m
- ω
- angular speed, rad/s = 2πN / 60
- N
- speed in rpm
Worked example
An engine making 250 N·m at 3500 rpm.
Inputs:
- Torque: 250 N·m
- Engine speed: 3500 RPM
The calculator gives:
- Result: 91.63 kW
- Power (Watts): 91629.8 W
- Power (Horsepower): 122.88 hp
Tips and common mistakes
- Peak torque and peak power happen at different rpm.
- 1 kW ≈ 1.341 hp.
- 1 lb·ft ≈ 1.356 N·m.
Questions people ask
How do I work this out in horsepower and lb·ft?
Use hp = torque (lb·ft) × rpm / 5252. That is why every torque and horsepower curve in lb·ft and hp crosses at 5252 rpm.
Why can a diesel have more torque but less power than a petrol engine?
Power is torque multiplied by speed. Diesels make high torque at low rpm but don’t rev as high, so their peak power can be lower even though they pull harder at low speed.
Which horsepower does the calculator use?
Mechanical horsepower, 1 hp = 745.7 W. Metric horsepower (PS or cv), used in many car brochures, is 735.5 W, so the same engine reads about 1.4 % higher in PS.
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