1/3 Motor

[Steven Hsieh]

When they say 1/3 hp motor, how much RPM is that?

[John Olbach]

hp has nothing to do with RPM ...

[Mike Henderson]

HP and RPM are apples and oranges. There's no real relationship between them.

There is a relationship between torque and HP. HP is a function of RPM and torque (and some constants). See Wikipedia's discussion of HP for more.

But a 1/3HP motor could run at 3450RPM, or 1725RPM, or any other speed, and it could still be rated at 1/3 HP. The slower it goes, the more torque is needed to produce the same HP, so the slower motor will be physically larger (for the same HP). That's why universal motors are so small - because they turn at a very high RPM compared to induction motors.

Mike