Horsepower Calculator

Calculate engine horsepower from torque and RPM or estimate HP from quarter mile time and vehicle weight. Convert between HP, kW, and metric horsepower.

Horsepower and torque are related but distinct measures of an engine's output -- torque is the rotational force the engine produces, while horsepower is the RATE at which that force does work, which is why engine speed (RPM) has to enter the calculation. This calculator's default method uses the standard SAE formula, Horsepower = (Torque x RPM) / 5252, a constant derived from the mechanical definition of horsepower (33,000 ft-lb of work per minute) combined with the relationship between rotational speed and linear work rate. Because RPM is a direct multiplier in that formula, the same torque figure produces more horsepower at higher engine speeds -- which is why high-revving engines can produce strong horsepower figures even with comparatively modest torque, while low-revving diesel engines often post huge torque numbers but more modest horsepower. The calculator's alternate method estimates horsepower purely from a vehicle's quarter-mile elapsed time and weight, using a classic empirical drag-strip formula (HP = Weight x (5.825/ET)^3) that back-calculates an approximate power figure from real-world acceleration performance rather than a dyno measurement -- useful for a rough estimate when only time-slip data is available, though it necessarily folds in traction, gearing, and driver skill alongside raw engine output. Results are also converted to kilowatts, metric horsepower (PS), and BTU per hour using standard fixed conversion factors.