Relationship between HP, RPM, and Torque

When designing a belt drive, the load being transmitted is one of the most important pieces of information that is needed.  To properly describe the load, there are two key pieces of information: HP and RPM, or Torque (Q) and RPM.  RPM is important in either case to quantify the load.  Believe it or not 10hp at 1000rpm is not a very high load compared to 10hp at 100rpm.  Here are the equations that relate one to the other:

This is for torque in in*lbs

HP = (Q x RPM) / 63025

Q = (HP x 63025) / RPM

This is for torque in ft*lbs

HP = (Q x RPM) / 5252

Q = (HP x 5252) / RPM

If we use the example above, the torque for 10hp at 1000rpm is 630.25 in*lbs, where the torque for 10hp at 100rpm is 6302.5 in*lbs, a pretty big difference for your belt drive!