Horsepower & Torque Calculator
Convert between horsepower and torque at a given RPM. Also calculate HP from trap speed or ET and vehicle weight.
HP and Torque Relationship
Horsepower and torque are mathematically related through RPM. Torque is the rotational force the engine produces. Horsepower is how fast that force is applied — it's work over time.
HP = (Torque × RPM) / 5252
At exactly 5,252 RPM, horsepower and torque are always equal. Below that RPM, torque is higher than HP. Above it, HP is higher than torque.
Trap Speed Method
The trap speed formula estimates wheel horsepower from your quarter-mile trap speed (the speed you cross the finish line at) and vehicle weight. This works because trap speed correlates closely with average power — it's less affected by traction than ET.
HP = Weight × (Trap Speed / 234)³
ET Method
The ET (elapsed time) formula estimates wheel HP from your quarter-mile time and vehicle weight. This method is more sensitive to traction and launch consistency than trap speed.
HP = Weight / (ET / 5.825)³
Wheel HP vs Crank HP
Both the trap speed and ET methods estimate wheel horsepower — the power actually reaching the ground. To estimate crank horsepower, add drivetrain losses: typically 15% for RWD manual, 17% for RWD auto, 20% for AWD.
Frequently Asked Questions
What is the difference between horsepower and torque?
Torque is rotational force — how hard the engine can twist the crankshaft, measured in lb-ft or Nm. Horsepower is the rate at which that force does work, calculated as torque × RPM ÷ 5252. Torque determines how quickly a vehicle accelerates from low speeds, while horsepower determines top speed and high-RPM pull.
How do you calculate horsepower from torque and RPM?
HP = (Torque × RPM) ÷ 5252, where torque is in lb-ft. For example, 400 lb-ft at 4000 RPM = (400 × 4000) ÷ 5252 = 304.6 HP. The constant 5252 comes from converting between units (33,000 ft-lb/min per HP divided by 2π).
What is the difference between crank HP and wheel HP?
Crank HP (BHP/flywheel HP) is measured at the engine output shaft. Wheel HP (WHP) is measured at the wheels on a dynamometer. The difference is drivetrain loss — typically 10-15% for rear-wheel drive, 15-20% for front-wheel drive, and 20-25% for all-wheel drive due to friction in the transmission, driveshaft, differential, and axles.
Related Calculators
Estimate quarter-mile elapsed time and trap speed from vehicle weight and horsepower. Includes 1/8 mile estimates.
0-60 TimeEstimate 0-60 mph time from horsepower, vehicle weight, and drivetrain type. Compares against common performance benchmarks.
Power/WeightCalculate power-to-weight ratio in HP/lb, HP/ton, kW/kg, and PS/kg. Compare against vehicle class benchmarks from economy cars to hypercars.
Dyno CorrectionCalculate dyno correction factors using SAE J1349, DIN 70020, and STD methods from temperature, barometric pressure, and humidity. Convert between corrected and observed HP.