Horsepower equals torque in lb-ft times engine speed in rpm, divided by 5252. An engine making 300 lb-ft at 6,000 rpm produces 300 × 6000 ÷ 5252 ≈ 342.7 hp, which is about 255.6 kW. From a drag strip run, hp ≈ weight × (trap mph ÷ 234)³ gives a wheel-power estimate instead.
Tuners reading a dyno sheet, buyers comparing spec sheets and drag racers checking a time slip all end up asking the same question: how much power is that? This calculator answers it three ways. Give it torque and the rpm where it was measured and it returns exact horsepower, since power is just torque multiplied by rotational speed. Give it the car's race weight with the driver plus a quarter-mile elapsed time or trap speed and it applies the Hale drag-strip formulas to estimate power. Each result is also shown in kilowatts and metric horsepower (PS). The drag-strip figures are estimates of power reaching the ground: launch traction, gearing, aerodynamics and air density all shift them, so treat them as a rough check, not a dyno reading.
Choose torque and rpm, quarter-mile time, or trap speed. Only the inputs that method needs are shown.
Use torque in lb-ft at a given rpm, or the race weight in pounds including the driver with your ET or trap speed.
Horsepower appears at the top with kilowatts and PS below, plus the working for each conversion.
Result Horsepower: 400
Kilowatts: 298.3
Metric horsepower (PS): 405.5
At 5,252 rpm the torque figure and the horsepower figure are the same number, which is why dyno curves cross there.
Result Horsepower: 342.7
Kilowatts: 255.6
Metric horsepower (PS): 347.5
300 × 6000 ÷ 5252 gives about 342.7 hp, or roughly 347 PS on a European spec sheet.
Result Horsepower: 437.5
Kilowatts: 326.2
Metric horsepower (PS): 443.6
117 ÷ 234 is exactly one half, and half cubed is 1/8, so the estimate is 3500 ÷ 8 = 437.5 hp at the wheels.
hp = T × rpm ÷ 5252; hp ≈ W × (5.825 ÷ ET)³; hp ≈ W × (v ÷ 234)³
TrpmWETvOne mechanical horsepower is 33,000 ft-lbf of work per minute. Power is torque times angular speed, and one revolution is 2π radians, so hp = T × rpm × 2π ÷ 33,000, which simplifies to T × rpm ÷ 5252. The two drag-strip formulas are empirical fits published by Roger Hale; trap speed tracks power more closely than ET because it is less affected by the launch. Kilowatts use 1 hp = 0.7457 kW and PS uses 1 PS = 0.7355 kW.
One horsepower is 33,000 foot-pounds per minute. Converting rpm to radians per minute multiplies by 2π, and 33,000 ÷ 2π is about 5252. That constant only works with torque in lb-ft and speed in rpm.
At exactly 5252 rpm the formula reduces to hp = T × 1, so both numbers are equal. Below that speed the torque figure is larger; above it horsepower is larger. Every dyno chart plotted in lb-ft and hp on the same scale shows this crossing.
It reflects power that actually moved the car, so it is closest to wheel horsepower. Crank output is higher by the drivetrain loss, often quoted around 10–20% depending on transmission and layout.
Trap speed. Elapsed time includes the launch, so a poor start, wheelspin or a slow shift adds time without saying anything about engine output. Trap speed is set mostly by power-to-weight over the back half of the track.
Mechanical horsepower is 745.7 W; metric horsepower (PS) is 735.5 W. So a figure in PS is about 1.4% larger than the same power in hp. European and Japanese brochures often quote PS.
Divide newton-metres by 1.3558. For example, 400 N·m is about 295 lb-ft. Enter that converted value in the torque field.
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). HP Calculator. Tools Directory. Retrieved October 28, 2026, from https://tools.milunir.com/automotive/engine-and-performance/hp-calculator/
Tools Directory Editorial Team. “HP Calculator.” Tools Directory, 13 Oct. 2026, https://tools.milunir.com/automotive/engine-and-performance/hp-calculator/. Accessed 28 Oct. 2026.
Tools Directory Editorial Team. “HP Calculator.” Tools Directory. Last modified October 13, 2026. Accessed October 28, 2026. https://tools.milunir.com/automotive/engine-and-performance/hp-calculator/.
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