Torque to Horsepower Calculator
Enter an engine's torque in pound-feet and its speed in rpm to get the power it produces, in both mechanical horsepower and kilowatts.
Use lb-ft, not Nm
The 5252 constant assumes torque in pound-feet. If your figure is in newton metres, convert it first (1 lb-ft ≈ 1.356 Nm) or the result will be off.
What is a torque-to-horsepower calculator?
Torque and rpm in, power out
A torque-to-horsepower calculator turns two engine figures — the torque in pound-feet and the engine speed in rpm — into power, the rate at which the engine does work. Torque on its own tells you how hard the crankshaft is twisting, but it says nothing about how fast. Power combines the two: the same torque produced at twice the rpm is twice the power. Enthusiasts use this to read a dyno chart, compare engines, or sanity-check a manufacturer's quoted figures, and the calculator also converts the result into kilowatts, the metric unit used on most spec sheets outside the US.
Enter the torque in lb-ft and the rpm to get the horsepower and kilowatts the engine is making at that point.
One core formula relates torque and rpm to power, and one conversion turns horsepower into kilowatts.
horsepower = (torque × rpm) / 5252The magic number 5252 is not arbitrary: it equals 33000 / (2π). One mechanical horsepower is defined as 33000 foot-pounds of work per minute, and dividing by 2π accounts for the radians in a full revolution. A direct consequence is that on any dyno graph the torque curve (in lb-ft) and the power curve (in hp) always cross at exactly 5252 rpm. To get kilowatts, multiply the horsepower by 0.7457.
Suppose an engine makes 300 lb-ft of torque at 5252 rpm.
Multiply torque by rpm
300 × 5252 = 1,575,600 — torque times engine speed.
Divide by 5252
1,575,600 / 5252 = 300 hp — the power output.
Convert to kilowatts
300 × 0.7457 = 223.71 kW — the same power in metric units.
The result tells you how much usable power the engine is producing at that exact rpm — and the relationship is the key insight. Below 5252 rpm an engine's horsepower is numerically lower than its torque; above 5252 rpm, horsepower is higher than torque. That is why high-revving engines can post big horsepower numbers from modest torque: they make their torque spin fast. A torquey diesel and a screaming sports-bike engine can reach the same peak horsepower by completely different routes — lots of torque at low rpm versus modest torque at very high rpm. Because power, not torque, sets how quickly work gets done, peak horsepower is the better single number for acceleration and top speed, while peak torque tells you more about low-end pulling feel. The kilowatt figure (223.71 kW for our 300 hp example) is simply the same power in SI units; one kilowatt is about 1.341 horsepower, so divide kW by 0.7457 to go back the other way.
The conversion is exact, but watch the units and remember what power figure you are reading.
Units and crank-versus-wheel power
The 5252 constant only works when the torque is in pound-feet; a newton-metre figure must be converted first (1 lb-ft ≈ 1.356 Nm). The result is also only as meaningful as the torque you enter — peak power needs the torque measured at peak-power rpm, not the engine's peak-torque figure at a different rpm. Finally, this gives brake (crankshaft) power for the torque you supply; drivetrain losses mean the power actually reaching the wheels is typically 10–20 % lower, and dyno numbers vary with correction standards (SAE, DIN, and others), so treat any single figure as approximate.