How to Calculate Horsepower
What is Horsepower?
Horsepower (HP) measures the rate of work an engine can perform. It is calculated from torque and RPM: HP = Torque × RPM / 5252. The constant 5252 comes from unit conversion (one horsepower = 550 ft-lb/sec × 60 sec × 2π).
Step-by-Step Guide
- 1Torque (lb-ft) measures rotational force at the crankshaft
- 2RPM is the engine speed in revolutions per minute
- 3HP = Torque × RPM / 5252
- 4Torque and HP curves cross always at 5,252 RPM
Worked Examples
Input
350 lb-ft torque at 5,000 RPM
Result
333 HP
350 × 5000 / 5252 = 333 HP
Input
400 HP, 4,500 RPM
Result
467 lb-ft torque
400 × 5252 / 4500 = 467 lb-ft
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