About this tool
The Horsepower Calculator works out engine power four different ways from whichever numbers you have. The classic dynamometer relationship is HP = Torque (lb·ft) × RPM / 5252, where 5252 is the RPM at which a curve's horsepower and torque lines always cross (it is 33,000 ft·lbf/min ÷ 2π). Enter torque in lb·ft or N·m (converted at 1 N·m = 0.7376 lb·ft) plus engine speed and you get brake horsepower and its kilowatt equivalent. The inverse mode back-solves torque from a known HP and RPM: Torque = HP × 5252 / RPM.
Two drag-strip estimators use the well-known Fox/Hale formulas that relate a car's power-to-weight to its quarter-mile performance. Trap-speed method: HP = Weight (lb) × (Trap mph / 234)³ — the speed the car is travelling as it crosses the finish line is a strong proxy for power. Elapsed-time method: HP = Weight (lb) / (ET seconds / 5.825)³. Both accept vehicle weight in pounds or kilograms and assume the weight includes the driver.
Everything runs locally in your browser — nothing is uploaded. These estimates are for comparison and tuning intuition, not certified figures: real crank output depends on air density, driveline losses, traction, and how the run was launched. The torque method is exact by definition; the drag-strip methods are empirical approximations that work best on stock-ish street cars.