Horsepower Calculator
Estimate engine horsepower from quarter-mile time and trap speed, or convert between HP, kW, and ft-lbs of torque.
Inputs
Horsepower
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Kilowatts
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PS (metric HP)
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HP per 1,000 lb
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Weight-to-power ratio
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About Horsepower Calculator
5252 RPM magic number
Torque and HP curves cross at 5252 RPM on any engine, because HP = T × RPM / 5252. It’s not a coincidence — it’s how the units are defined: 1 HP = 550 ft-lb/s, and 33,000 ft-lb/min ÷ 2π ≈ 5252.
Hale vs ET formula
Hale (using trap speed) is more accurate because it depends on energy actually delivered to the wheels. ET-based estimates are off when there’s wheel-spin or unusual gear ratios.
Crank vs wheel HP
Crank HP is measured at the engine. Wheel HP (RWHP/AWHP) is what reaches the ground after drivetrain losses (10-20%). Most magazine reviews quote crank; chassis dynos give wheel.