S% = ((Ns - Nr) / Ns) * 100
SRPM = Ns - Nr
Where：
S = Motor slip
Ns = Synchronous speed (RPM)
Nr = Rotor speed (RPM)
Calculate AC induction motor slip (%) and slip in RPM from synchronous speed and rotor speed. Understand slip's role in torque production. For engineers, technicians, and students.
This tool uses the standard slip formula:
Slip (%) = (N s – N r) / N s × 100%
Slip (RPM) = N s – N r
Note: You must provide both Ns and Nr. The calculator does not compute synchronous speed from frequency or poles, nor does it reverse-calculate rotor speed from slip.
Input: Synchronous speed = 3000 RPM, Rotor speed = 2850 RPM
Output: Slip = (3000 – 2850) / 3000 × 100% = 5% (or 150 RPM)
Tip: Synchronous speed can be estimated using Ns = (120 × f) / P, where f = supply frequency (Hz) and P = number of poles. This pre-calculation is required before using this tool.
| Motor Type | Full-Load Slip Range |
|---|---|
| Fractional HP Motors | 5% – 8% |
| Standard Industrial Motors (1–100 HP) | 2% – 5% |
| High-Efficiency Motors | 1% – 3% |
| High-Slip Motors (e.g., crushers, conveyors) | 8% – 15% |
Slip increases with mechanical load. At no-load, it may be as low as 0.5%; at full load, it reaches its rated value.
Rotor speed (Nr) is always lower than synchronous speed (Ns) in an induction motor.
Prolonged operation with slip >8% may indicate overload, low voltage, bearing wear, or mechanical binding—and can lead to overheating.
This tool estimates slip only. It does not model dynamic behavior, harmonics, or VFD effects.
Verifying expected slip during motor performance checks
Supporting troubleshooting when abnormal motor speeds are observed
Teaching fundamental induction motor principles in labs or classrooms
Providing input data for efficiency or thermal analysis workflows
Maintenance technicians measuring motor speed in the field
Electrical engineers validating motor operating points
Students and educators learning about slip and torque production
Facility staff documenting motor performance during audits
Slip is the difference between the synchronous speed of the stator’s rotating magnetic field and the actual rotor speed. It enables current induction in the rotor, which produces torque. Without slip, the motor cannot generate torque.
Not always. High-slip motors (e.g., for conveyors or crushers) are designed to operate at 8–15% slip. However, if a standard motor shows slip >8% under normal load, it may indicate a problem such as overload or voltage drop.
Use with caution. VFDs alter frequency and waveform, which affects slip interpretation. This calculator assumes a sinusoidal supply at fixed frequency. For VFD applications, additional harmonic and control considerations apply.
Synchronous speed (in RPM) is calculated as Ns = (120 × f) / P, where f is the supply frequency (e.g., 50 Hz or 60 Hz) and P is the number of magnetic poles. Example: 4-pole motor at 50 Hz → Ns = (120 × 50) / 4 = 1500 RPM.
Login
