Torque to hp Calculator
Work out horsepower from torque and rpm, or torque from horsepower and rpm.
Power at 406.7 N·m across the rev range
| Speed | Horsepower | Kilowatts |
|---|---|---|
| 1,000 rpm | 57.1 hp | 42.59 kW |
| 2,000 rpm | 114.2 hp | 85.19 kW |
| 3,000 rpm | 171.4 hp | 127.78 kW |
| 4,000 rpm | 228.5 hp | 170.38 kW |
| 5,252 rpm | 300 hp | 223.71 kW |
| 6,000 rpm | 342.7 hp | 255.57 kW |
| 7,000 rpm | 399.8 hp | 298.16 kW |
Power is torque times speed
Torque is twisting effort; power is how fast that effort does work. In SI:
P (W) = τ (N·m) × ω (rad/s), where
ω = rpm × 2π ÷ 60
In imperial units the constants collapse into the well-known shortcut:
hp = lb-ft × rpm ÷ 5252
lb-ft = hp × 5252 ÷ rpm
Where 5252 comes from
One horsepower is 33,000 ft-lb per minute. A full turn is 2π radians, so
33,000 ÷ 2π = 5252.1. It is not an arbitrary number — it is
the unit conversion baked into a single constant.
A consequence: torque and horsepower are numerically equal at 5252 rpm, always. That is why dyno graphs for petrol engines cross at that point, and it is a quick sanity check on any published figure.
Reading a dyno chart
Torque usually peaks in the mid range and falls off as valve timing and breathing run out. Power keeps climbing after peak torque, because the rising rpm more than compensates for falling torque — until torque drops fast enough to overcome it. Peak power therefore always occurs at higher rpm than peak torque.
This is shaft power at the stated speed. Wheel horsepower is lower after drivetrain losses, typically 10-15% for a manual gearbox and more for an automatic.