Induction Motor Slip

How to use this calculator

An induction motor's stator field rotates at the synchronous speed ns = 120·f / P (f in Hz, P = number of poles). The rotor always runs slightly slower; the difference is the slip: s = (ns − nr) / ns. Enter the supply frequency, number of poles, and the actual rotor speed, and the calculator computes the synchronous speed (if you didn't enter it), the slip as a fraction and percentage, and the slip frequency f_slip = s·f.

What it means in a real circuit

For a 4-pole, 50 Hz motor, ns = 120×50/4 = 1500 rpm. If the rotor runs at 1450 rpm, slip = (1500−1450)/1500 = 3.3%, and the slip frequency is 1.65 Hz. Slip is what produces torque: with zero slip there's no relative motion and no induced rotor current, hence no torque. Typical full-load slip is 2–5%. Use this to verify a motor's speed, diagnose a slow-running motor (high slip), or compute the rotor-frequency for analysis.