Horsepower Calculator
Calculate horsepower from torque and RPM, or from elapsed time and trap speed.
About Horsepower Calculator
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
Worked example
With the default values below, Horsepower Calculator returns Horsepower of 300.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Solve Forone of Horsepower (from torque & RPM), Torque (from HP & RPM), RPM (from HP & torque)
- Horsepower (from torque & RPM)
- Torque Unitone of lb·ft (pound-feet), N·m (Newton-metres)
- lb·ft (pound-feet)
- Torqueaccepts 0–10,000
- 300
- Engine Speed (RPM)accepts 1–20,000 RPM
- 5,252 RPM
- Horsepower (HP)accepts 0–10,000 HP
- 300 HP
Results
- Horsepower
- 300.00 HP
- Kilowatts
- 223.71 kW
- Torque
- 300.00 lb·ft
- Torque
- 406.75 N·m
- RPM
- 5,252 RPM
Step by step
- 1Torque in lb·ft= 300 lb·ft
- 2HP = Torque × RPM ÷ 5252= 300 HPAt 5252 RPM, torque (lb·ft) and horsepower are always equal.
- 3Kilowatts= 223.71 kW
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.