🏎️ Horsepower Calculator

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Horsepower measures the rate of doing work, and this horsepower calculator finds it two ways. In the first mode, engine power follows directly from torque and rotational speed: HP = torque (lb-ft) × RPM ÷ 5252. The magic number 5,252 comes from the definition of horsepower (33,000 ft-lb per minute) and the 2π radians in a revolution, and it is also the RPM at which the horsepower and torque curves always intersect on a dyno chart. The tool reports the metric equivalent too, using 1 hp = 0.7457 kW.

As a worked example, an engine making 300 lb-ft of torque at 5,000 RPM produces 300 × 5000 ÷ 5252 ≈ 286 hp, which is about 213 kW. Because power is torque times speed, the same 300 lb-ft makes far more horsepower at high RPM than at low — which is why high-revving engines chase big peak-power figures even with modest torque.

Switch to the quarter-mile mode to estimate drag-strip performance from power and vehicle weight using Roger Huntington’s classic empirical formulas: trap speed ≈ 234 × (hp / weight)^⅓ mph and elapsed time ≈ 5.825 × (weight / hp)^⅓ seconds. A 300 hp car weighing 3,500 lb comes out around 103 mph and a 13.2-second quarter mile. These are rough guides that ignore traction, aerodynamics and driver skill, but they are a quick sanity check for a build or a way to back out power from a known trap speed.