Horsepower & Torque Converter

Enter any two of HP, torque, and RPM to calculate the third.

Horsepower (HP)

Torque (lb-ft)

RPM

Horsepower —

Torque —

RPM —

Kilowatts —

Newton-meters —

HP = Torque × RPM / 5252. At 5,252 RPM, HP and torque are always equal. Below that RPM, torque exceeds HP; above it, HP exceeds torque.

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Power Conversions

From	To	Multiply by
HP	kW	0.7457
kW	HP	1.341
lb-ft	Nm	1.3558
Nm	lb-ft	0.7376
HP (metric/PS)	HP (SAE)	0.9863

The HP-Torque-RPM Relationship

Horsepower and torque are related through RPM: HP = Torque (lb-ft) × RPM / 5252. This means you can calculate any one of the three if you know the other two.

Torque is the rotational force the engine produces. Horsepower is the rate at which that force does work. A diesel truck has high torque at low RPM; a sport bike has high HP at high RPM.

Horsepower and torque are related by engine RPM: HP = (torque × RPM) / 5252. The constant 5252 comes from converting ft-lb/min to horsepower (1 HP = 33,000 ft-lb/min, divided by 2π gives 5252). At 5252 RPM, horsepower and torque (in ft-lb) are numerically equal.

Example: an engine making 300 ft-lb at 4,000 RPM produces (300 × 4000) / 5252 = 228 HP. The same engine at 6,000 RPM making 280 ft-lb produces (280 × 6000) / 5252 = 319 HP — peak power occurs at higher RPM even though torque has fallen.

Torque determines initial acceleration force; horsepower determines sustained top speed and high-RPM acceleration. Diesel engines make high torque at low RPM (useful for towing and off-road); high-revving gasoline engines make peak power at high RPM where the power band is narrow.

Dyno curves: production cars are typically rated at crankshaft (flywheel) HP/torque. Wheel horsepower (measured at the wheels) is 10–20% lower due to drivetrain losses (transmission, driveshaft, differentials). Front-wheel-drive cars lose approximately 10–13%; rear-wheel-drive 12–15%; all-wheel-drive 15–20%.