Convert between horsepower and torque at a given engine speed, in both directions: horsepower plus RPM gives torque, and torque plus RPM gives horsepower.
Horsepower to torque
Torque to horsepower
Horsepower and torque are linked by engine speed: horsepower equals torque in lb-ft multiplied by RPM, divided by 5252. Rearranged, torque equals horsepower multiplied by 5252 and divided by RPM. The constant 5252 is where the two curves cross: at exactly 5252 RPM, the horsepower and torque figures in lb-ft are always numerically equal, which is why dyno charts plotted on matching scales always cross at that speed. Torque in newton-metres is the lb-ft figure multiplied by 1.35582. A single horsepower or torque peak figure says nothing about the other without the RPM at which it occurs, which is why both numbers and their speeds are needed for a meaningful comparison.
What is the formula linking horsepower and torque? Horsepower equals torque (lb-ft) multiplied by RPM divided by 5252. To go the other way, torque equals horsepower multiplied by 5252 divided by RPM.
Why do horsepower and torque cross at 5252 RPM? Because 5252 is the constant in the formula. At 5252 RPM the division cancels out, so horsepower and torque in lb-ft are numerically equal at that speed for any engine.
How is torque in lb-ft converted to newton-metres? Multiply by 1.35582. One pound-foot is about 1.356 newton-metres, and one newton-metre is about 0.738 pound-feet.