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Torque does the work; horsepower tells you how fast.
Horsepower and torque are the same measurement at different speeds, welded together by one constant: HP = T × RPM ÷ 5,252. This calculator solves either direction and converts to kilowatts and newton-meters — for sizing motors, reading dyno sheets, or winning arguments about diesels.
Mechanical engineers and mechanics use it both directions: motor sizing from load torque, and decoding dyno sheets where peak torque and peak power happen at different RPM. Also settles bar arguments about why diesels tow.
One horsepower is defined as 33,000 ft·lb per minute. A pound-foot of torque acting through one revolution does 2π ft·lb of work, so HP = T × 2π × RPM ÷ 33,000 = T × RPM ÷ 5,252 (rounded). Every torque and horsepower curve on every dyno chart crosses at exactly 5,252 RPM — it is arithmetic, not coincidence.
No — gearing trades RPM for torque at roughly constant power (minus friction losses, typically 2–15%). A 3:1 reduction triples output torque at one-third the speed. This is why electric motors with flat torque curves need fewer gears than engines with peaky ones.
Start from the load torque at the required speed, compute HP here, then apply a service factor (1.15–1.25 typical) for starts, ambient temperature, and duty cycle. Size to the worst operating point, not the nameplate average — and check starting torque separately; it is often 2–3× running torque.