Horsepower Torque Calculator
Power and torque are the same information at a given rpm - convert between hp, kW or PS and lb-ft or Nm, solve for whichever of the three is missing, and see why every dyno graph crosses at 5252.
Enter Power, Torque and RPM
Conversion Result
Your torque across the rev range
| RPM | Horsepower | Kilowatts |
|---|
The 5252 crossing, drawn
Where 5252 comes from
James Watt defined one horsepower as 33,000 foot-pounds of work per minute. Rotating work is torque times angle, and one revolution is 2 pi radians, so power in foot-pounds per minute is torque x rpm x 2 pi. Divide by 33,000 and you get horsepower = torque x rpm / 5252, because 33,000 / (2 pi) = 5252.113. Nothing in that number is empirical or tuned, which is why this page carries no accuracy warning - a rarity in this section. The only spread in the answer is the spread in your inputs. Metric wears different clothes for the same idea: kW = Nm x rpm / 9549.3. And PS, the European and Japanese metric horsepower, is defined as 735.49875 W, about 1.4% smaller than the mechanical hp - which is why a 300 PS engine is 296 hp, not 300.
Why every dyno graph crosses at 5252 rpm
Plot torque in lb-ft and power in hp on the same numeric scale and the curves must intersect at 5252 rpm, because that is the rpm where the equation makes the two numbers equal. Below 5252 the torque number is always the larger one, above it the horsepower number is. If a dyno sheet in lb-ft shows the curves crossing somewhere else, or not crossing at all, the plot is using two separate y-axes. The part most explainers skip: the crossing is a property of the units, not the engine. Nothing mechanical happens at 5252 rpm. Draw the same engine in Nm and kW and the crossing moves to 9549 rpm, past the redline of nearly everything with four wheels.
Torque or horsepower - which one matters
They are not rivals: at any rpm, either number determines the other, and this converter is the proof. What accelerates a car is torque at the wheels, and gearing multiplies torque - a shorter gear trades rpm for wheel torque. That is why the engine that wins is the one holding the most power across the rev range it actually uses: power is what survives the gearbox. If you want to know what your engine really makes, work backwards from a time slip with the horsepower from trap speed calculator, see what a given power gets you with the quarter mile calculator, or estimate what forced induction would add with the boost to horsepower calculator.