Horsepower Calculator
Enter torque and RPM to compute horsepower, or switch to the trap-speed method.
Horsepower from an engine's torque and speed is torque in pound-feet times RPM, divided by 5,252 — the RPM at which torque and horsepower are always equal. An engine making 400 lb-ft at 5,000 RPM produces 400 × 5,000 ÷ 5,252 ≈ 381 horsepower.
How to Use This Calculator
Choose your method. The torque-and-RPM method computes horsepower directly from a dyno-style torque figure and engine speed. The trap-speed method estimates horsepower from a vehicle's weight and its quarter-mile trap speed, useful when you have run the car but not measured torque.
Enter the values for the method you picked and the calculator returns the horsepower, switching the input fields to match your choice.
How the Calculation Works
Power is the rate of doing work, which for a rotating engine is torque times rotational speed. Converting the units of pound-feet and RPM into horsepower introduces the constant 5,252 — the RPM where the torque and horsepower curves always cross.
The trap-speed method uses an empirical drag-racing relationship: horsepower scales with vehicle weight and the cube of trap speed divided by 234. It is an estimate, since it folds in aerodynamics and driveline losses.
HP = torque × RPM ÷ 5252; trap: HP = weight × (mph ÷ 234)³
Worked Example
An engine producing 400 lb-ft of torque at 5,000 RPM makes 400 × 5,000 ÷ 5,252 = 380.8 horsepower.
Using the trap-speed method, a 3,000 lb car trapping 110 mph estimates 3,000 × (110 ÷ 234)³ = 3,000 × 0.104 ≈ 312 horsepower at the wheels.
Assumptions and Limitations
- Torque method needs torque at a specific RPM (as from a dyno)
- 5,252 is exact for lb-ft and RPM to mechanical horsepower
- Trap-speed method is an estimate that includes aero and driveline losses
- Flywheel vs wheel horsepower differ by the drivetrain loss
Who Uses a Horsepower Calculator
Gearheads, tuners, and students use this to find horsepower from torque and RPM, or from a vehicle's trap speed. Run it after a dyno or drag pass, while planning a build, or to understand the torque-power relationship. Enter your figures to get the estimated horsepower.
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Open calculator →Frequently Asked Questions
How do you calculate horsepower from torque?
Multiply torque in pound-feet by RPM, then divide by 5,252. So 400 lb-ft at 5,000 RPM is 400 × 5,000 ÷ 5,252 ≈ 381 hp.
Why 5,252?
It comes from converting torque in lb-ft and rotational speed in RPM into horsepower. It is also the RPM at which an engine's torque and horsepower values are always numerically equal.
How do you estimate horsepower from trap speed?
Use HP = weight × (trap speed ÷ 234)³. It is an empirical drag-racing formula that estimates power from a quarter-mile run when you don't have dyno data.
What is the difference between wheel and flywheel horsepower?
Flywheel (crank) horsepower is measured at the engine; wheel horsepower is what reaches the ground after drivetrain losses of roughly 10–20%. Trap-speed estimates are closer to wheel horsepower.
Does more torque mean more horsepower?
Not directly — horsepower depends on torque and RPM together. A high-revving engine can make big horsepower from modest torque, while a diesel makes strong torque at low RPM.
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