Horsepower equals torque in lb-ft times engine speed in rpm, divided by 5,252. An engine making 300 lb-ft at 5,252 rpm produces 300 hp, or 223.7 kW. From a drag strip slip, a 3,000 lb car trapping 117 mph is putting about 375 hp to the wheels.
Spec sheets quote torque at one rpm and power at another, and drag strip slips give only times and speeds. This calculator turns any of those into horsepower. Pick torque and rpm to convert a dyno reading, in lb-ft or N·m, into horsepower at that engine speed. Pick quarter-mile ET or trap speed and enter the race weight including the driver to estimate the power the car must be making to run those numbers. Every result is also shown in kilowatts and metric horsepower (PS) with the working laid out. The drag strip methods are empirical fits: launch technique, gearing, aerodynamics and track conditions all move the answer, so treat them as a ballpark of wheel power rather than a dyno figure.
Torque and rpm for a dyno or spec-sheet figure; ET or trap speed for a timeslip.
Set the torque unit to lb-ft or N·m inside the torque field, then type the engine speed where that torque was measured.
Use the race weight with driver and fuel, then the elapsed time or trap speed from the same pass.
The working under the result shows each constant used.
Result Horsepower: 300.0
Kilowatts (kW): 223.7
Metric horsepower (PS): 304.2
At 5,252 rpm the torque figure in lb-ft and the horsepower figure are the same number, which is why dyno curves cross there.
Result Horsepower: 375.0
Kilowatts (kW): 279.6
Metric horsepower (PS): 380.2
An 11.65-second pass at 3,000 lb works out to about 375 hp at the wheels.
Result Horsepower: 375.0
Kilowatts (kW): 279.6
Metric horsepower (PS): 380.2
Trap speed tracks power more closely than ET because it is less affected by launch and traction.
hp = T × rpm ÷ 5252; hp = W ÷ (ET ÷ 5.825)³; hp = W × (v ÷ 234)³
TrpmWETvOne mechanical horsepower is 550 ft-lbf per second. Power is torque times angular speed, and converting rpm to radians per second gives the constant 33,000 ÷ 2π, about 5,252. The two drag strip formulas are Roger Hale's empirical fits to quarter-mile data; they return power at the wheels. Kilowatts use 1 hp = 0.7457 kW, and PS uses 1 PS = 0.7355 kW.
A horsepower is 33,000 ft-lbf per minute. One revolution turns the crank through 2π radians, so power in hp is torque times rpm times 2π divided by 33,000, which simplifies to torque times rpm divided by 5,252. At exactly 5,252 rpm the two numbers match.
Wheel horsepower. The formulas were fitted to how fast cars of a given weight actually run, so drivetrain losses are already baked in. To guess crank power, people commonly add 10 to 20 percent depending on whether the car is rear, front or all-wheel drive.
Trap speed. Elapsed time depends heavily on the launch, tyre grip and the 60-foot time, while trap speed reflects how hard the car is pulling at the top of the run. A poor launch can add half a second to ET while barely changing trap speed.
Mechanical horsepower (hp) is 745.7 W; metric horsepower (PS, from the German Pferdestärke) is 735.5 W. So a 300 hp engine is about 304 PS. European spec sheets often use PS or kW, US ones use hp.
Yes. Switch the unit inside the torque field to N·m and the value is divided by 1.35582 to get lb-ft before the 5,252 formula is applied. For example, 400 N·m at 4,000 rpm gives about 224.7 hp.
The weight as the car crossed the line: the car with fuel, the driver and anything carried. Corner-weighing scales at the track give the best figure. Using a lighter brochure curb weight makes the result read low.
Using this tool in an assignment, article or report? Copy a citation, or a link for your website.
Tools Directory Editorial Team. (2026, October 13). Horsepower Calculator. Tools Directory. Retrieved October 26, 2026, from https://tools.milunir.com/automotive/engine-and-performance/horsepower-calculator/
Tools Directory Editorial Team. “Horsepower Calculator.” Tools Directory, 13 Oct. 2026, https://tools.milunir.com/automotive/engine-and-performance/horsepower-calculator/. Accessed 26 Oct. 2026.
Tools Directory Editorial Team. “Horsepower Calculator.” Tools Directory. Last modified October 13, 2026. Accessed October 26, 2026. https://tools.milunir.com/automotive/engine-and-performance/horsepower-calculator/.
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