Calculate horsepower from torque and RPM, or from elapsed time and trap speed.
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.
Horsepower from torque and RPM
HP = (Torque in lb·ft × RPM) ÷ 5252
Torque conversion
N·m = lb·ft × 1.35582
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.
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).
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.
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.