Convert HP to torque or torque to HP at any RPM using the SAE formula printed on every dyno sheet. Enter any two values to find the third.
Torque → HP (reverse)
Shows how HP changes across the RPM range if torque stays constant - useful for understanding the crossover point.
| RPM | Torque (lb·ft) | HP |
|---|
Horsepower and torque are not independent measurements - they are linked by RPM through a fixed mathematical relationship. One is always derivable from the other if you know the engine speed.
The constant is approximately 5252.113 for mechanical horsepower and lb-ft. Their numerical values therefore cross at about 5,252.1 RPM when plotted on the same scale.
Torque does the work - it's the twisting force that accelerates the car. Horsepower is the rate at which that work is done. In practical terms:
Modern ratings (post-2005) use SAE Net - power measured at the crankshaft with all accessories fitted (alternator, power steering pump, AC, etc.). Older "gross" ratings excluded accessories and often overstated output by 10-20%. Always specify when comparing.
Dynos measure at the wheels. Drivetrain losses (transmission, differential, axles) typically subtract 12-18% for RWD, 15-20% for AWD. A 400 WHP car is roughly 460-480 crank HP on a typical RWD platform.
It is worth stressing that drivetrain loss is not a fixed horsepower number - it scales with how much power is flowing through the driveline and with how the dyno operator calculates the "correction." Quoting a flat percentage is a convention, not a precise measurement. When you compare two cars, the only honest comparison is wheel-to-wheel on the same type of dyno, because crank figures are estimates layered on top of estimates.
The crossover falls out of the units. Since HP = torque × RPM / 5252.113, their numerical values are equal at approximately 5,252.1 RPM. This assumes lb-ft and mechanical horsepower plotted on the same scale.
Suppose a dyno shows your engine making 350 lb·ft of torque at 3,500 RPM. Plug it into the formula:
Now imagine torque has fallen to 300 lb·ft by 6,500 RPM as the engine runs out of breath up top. Even though torque dropped, horsepower keeps climbing because RPM rose faster than torque fell:
So peak torque was down low at 3,500 RPM, but peak power lands much higher in the band - a textbook illustration of why the two peaks rarely coincide. Notice also that at 3,500 RPM the HP number (233) is below the torque number (350), while a calculation at any RPM above 5252 would put HP above torque - the crossover at 5252 in action.
Because HP = Torque × RPM / 5252.113. The constant comes from the mechanical-horsepower and angular-speed unit conversion, so the numerical values cross at about 5,252.1 RPM.
Dynos measure power at the wheels, after drivetrain losses. RWD cars typically lose 12-18% between the crank and wheels; AWD cars 15-20%. A 400 WHP RWD car is roughly 460-480 HP at the crank.
Torque is the instantaneous twisting force, but horsepower is the rate of doing work - it already folds in how fast the engine is spinning. Because gearing multiplies torque, what actually determines acceleration at any road speed is the power available, since power is conserved through the gearbox while torque is not. That is why two engines with identical peak torque but different peak RPM accelerate very differently: the higher-revving one makes more horsepower.
Multiply mechanical (SAE) horsepower by 0.7457 to get kilowatts, or divide kilowatts by 0.7457 to get horsepower. So 400 HP is about 298 kW. Metric PS (used on many European spec sheets) is slightly different - 1 PS is about 0.9863 HP - so a 400 PS car is roughly 395 HP.
Not necessarily. Because HP = torque × RPM / 5252.113, horsepower rises while the RPM increase outweighs the torque decrease, so the peaks commonly occur at different engine speeds.
It is a unit-conversion result. With lb-ft and mechanical horsepower, HP = torque × RPM / 5252.113, so their numerical values are equal near 5,252.1 RPM.
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