Horsepower Calculator
Calculate horsepower from torque and RPM, or find torque from HP and RPM.
Inputs
Horsepower
300.00HP
Kilowatts
223.71kW
Torque
300.00lb·ft
Torque
406.75N·m
RPM
5,252RPM
Step by step
Torque in lb·ft
= 300 lb·ft
HP = Torque × RPM ÷ 5252
300 × 5252 ÷ 5252
= 300 HP
At 5252 RPM, torque (lb·ft) and horsepower are always equal.
Kilowatts
300 × 0.7457
= 223.71 kW
How it works
Horsepower is a measure of how quickly an engine can do work. Torque is rotational force; RPM is how fast the engine spins. Power = torque × angular velocity. In US customary units, 1 HP = 550 ft·lbf/s, which yields the constant 5252 (= 33,000 ÷ 2π) in the HP–torque–RPM triangle. At exactly 5252 RPM, an engine's torque in lb·ft numerically equals its horsepower.
Formulas
Horsepower from torque and RPM
HP = (Torque in lb·ft × RPM) ÷ 5252
- 5252
- 33,000 / (2π) — converts ft·lbf/min to HP
- T_lb·ft
- Torque in pound-feet
- RPM
- Engine speed in revolutions per minute
Torque conversion
N·m = lb·ft × 1.35582
Frequently Asked Questions
Why is the magic number 5252?
It comes from the definition of mechanical horsepower (550 ft·lbf/s): Power = Torque × angular velocity = T × (2π × RPM / 60). Rearranging HP = T × RPM / (550 × 60 / 2π) = T × RPM / 5252.11. At 5252 RPM, torque and HP are numerically equal on a dyno graph.
What's the difference between horsepower and torque?
Torque is the rotational force available, which determines acceleration from rest. Horsepower is the rate of delivering that work, which determines top speed and sustained acceleration. High torque at low RPM = pulling power (trucks); high HP at high RPM = sustained speed (sports cars).
How do I convert HP to kW?
1 mechanical HP = 0.7457 kW (exactly, by SI definition). Multiply HP by 0.7457 for kW, or divide kW by 0.7457 for HP.
My car's torque is in N·m. How do I use this calculator?
Select N·m in the Torque Unit dropdown. The calculator converts internally to lb·ft before applying the formula, then shows results in both units.