Peripheral Speed is an important factor in design. The peripheral speed refers to the speed on the periphery or the circumference of the rotor. The peripheral speed is given by the product of the circumference and the speed.

The formula for peripheral speed is

**Peripheral Speed = ? x D**

where D is the diameter of the rotor

The peripheral speed depends on the speed as well as the diameter of the rotor. If the peripheral speed is high, the windage losses will be more. This is an important factor in electric machine design.