Horsepower Calculator — Torque & RPM to HP, kW, PS
Convert engine torque and RPM to horsepower instantly, and see the full power curve across the rev range. Also shows kilowatts, metric HP (PS/CV), and watts.
ft·lbf
RPM
HP = Torque (ft·lbf) × RPM ÷ 5252
- 1
Torque × RPM
300 × 4,000 = 1,200,000 - 2
Horsepower
1,200,000 ÷ 5252 = 228.5
How does this calculator work?
Horsepower = Torque (ft·lbf) × RPM ÷ 5252. At 5,252 RPM torque and HP are numerically equal. One mechanical HP = 745.7 W = 0.7457 kW ≈ 1.014 metric PS. Enter torque and RPM to get HP, kW, metric HP, and a power-vs-RPM curve.
Formula
How this is calculated
Horsepower is a unit of power — the rate of doing work. James Watt defined one mechanical horsepower as 33,000 foot-pounds of work per minute (lifting 33,000 lbs by one foot every minute). Translating that to rotational motion: HP = Torque (ft·lbf) × RPM / 5252, where 5252 = 33,000 / (2π). So at 5,252 RPM, torque and horsepower figures are numerically equal — this crossover point appears on every dyno chart.
The power curve shows how HP scales linearly with RPM at constant torque. In a real engine, torque peaks at a certain RPM then falls off as breathing efficiency drops, so the power curve also peaks. This calculator plots the ideal (constant-torque) case to show the relationship.
Unit conversions: 1 mechanical HP = 745.7 W = 0.7457 kW. The metric horsepower (PS or CV, from German Pferdestärke or French cheval vapeur) is defined as 75 kgf·m/s = 735.5 W, so 1 mechanical HP ≈ 1.014 metric HP. European car specs typically quote PS, while US and UK specs use mechanical HP.
Frequently asked questions
Because 5,252 is 33,000 ÷ (2π). Power in hp = torque (ft·lbf) × RPM ÷ 5252. At exactly 5,252 RPM the divisor equals the RPM, leaving HP = torque numerically. This is why every engine dyno chart shows the torque and HP lines crossing at 5,252 RPM — it's a mathematical identity, not a performance sweet spot.
Mechanical (or imperial) horsepower = 745.7 W, defined via 33,000 ft·lbf/min. Metric horsepower (PS, CV, or hp(M)) = 735.5 W, defined as lifting 75 kg one metre in one second under standard gravity. The difference is about 1.4 %. Car specs from Germany, France, Italy, and Japan traditionally use PS; UK and US use mechanical HP. At high-power levels the gap matters (e.g. 500 PS ≈ 493 HP).
Check the manufacturer's power spec sheet — it usually lists peak torque (e.g. 300 ft·lbf at 3,500 RPM) and peak horsepower (e.g. 350 HP at 6,000 RPM). For an accurate curve, a chassis dynamometer (dyno) measures torque at every RPM under load. Aftermarket tune shops routinely produce dyno sheets for modified engines.
TG we-Calculate Editorial Team. (2026). Horsepower Calculator — Torque & RPM to HP, kW, PS [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/horsepower-calculator
TG we-Calculate Editorial Team. "Horsepower Calculator — Torque & RPM to HP, kW, PS." TG we-Calculate. 2026. https://we-calculate.com/calculator/horsepower-calculator.
TG we-Calculate Editorial Team, "Horsepower Calculator — Torque & RPM to HP, kW, PS," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/horsepower-calculator
@misc{wecalculate_horsepower_calculator, title = {Horsepower Calculator — Torque & RPM to HP, kW, PS}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/horsepower-calculator}}, year = {2026}, note = {TG we-Calculate} }
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