Motor Slip Frequency Calculator

A motor slip frequency calculator converts motor Slip from a percentage into hertz. The result is the electrical-frequency difference between the stator’s rotating magnetic field and the rotor of an induction motor.

Enter Supply frequency and Slip to calculate Slip frequency. For a motor operating from a 60 Hz supply with 3.333333% slip, the slip frequency is 2 Hz.

This calculation is useful when a motor or variable-frequency drive review needs slip expressed as frequency rather than as a percentage of synchronous speed. It does not diagnose motor condition, establish drive tuning, or replace motor test data.

Slip Frequency in Induction Motors

An induction motor rotor does not normally turn at synchronous speed while carrying load. The stator produces a rotating magnetic field based on the applied electrical frequency, while the rotor operates slightly below that speed. The difference is slip.

Slip can be reported as:

• A percentage of synchronous speed
• Rotor slip frequency in Hz

At standstill, rotor speed is zero and slip is 100%, so rotor slip frequency equals the applied stator frequency. As the motor accelerates toward synchronous speed, slip decreases. Under normal loaded operation, the slip frequency is much lower than the supply frequency.

Slip frequency can be used when reviewing induction motor operating behavior, VFD command conditions, rotor-frequency relationships, or motor-control calculations that reference frequency rather than percent slip.

Calculation Inputs and Results

Calculator field	Electrical meaning
Supply frequency	The motor supply or commanded electrical frequency, entered in Hz
Slip	Slip as a percentage of synchronous speed
Slip frequency	The calculated slip frequency, in Hz
Frequency used	The Supply frequency value used for the result
Slip used	The Slip percentage used for the result

The Supply frequency field may represent utility-frequency operation, such as 60 Hz, or the commanded output frequency of a VFD. For a drive-fed motor, use the actual commanded electrical frequency being reviewed—not automatically the building service frequency.

Slip Frequency Formula

The calculator uses:

\(\displaystyle \text{Slip frequency (Hz)} = \text{Supply frequency (Hz)} \times \frac{\text{Slip (\%)}}{100}\)

Where:

• Supply frequency is the applied or commanded motor electrical frequency.
• Slip is entered as a percentage.
• Slip frequency is the resulting frequency in hertz.

The result is proportional to both inputs. A higher applied frequency produces a higher slip frequency for the same slip percentage. Likewise, a higher slip percentage increases slip frequency at the same supply frequency.

Calculation Example

Given the following values:

Field	Value
Supply frequency	60 Hz
Slip	3.333333%

\(\displaystyle \text{Slip frequency} = 60 \times \frac{3.333333}{100} = \text{Slip frequency} \approx 2\text{ Hz}\)

The calculator result is:

Result	Value
Slip frequency	2 Hz
Frequency used	60 Hz
Slip used	3.3333%

A 2 Hz slip frequency means the rotor is operating with a 2 Hz frequency difference relative to the 60 Hz rotating stator field.

Motor and Drive Review Limits

Slip frequency is not the same as motor current, branch-circuit ampacity, feeder loading, voltage drop, raceway fill, conductor AWG or kcmil selection, or overload setting. Those decisions require the applicable motor data, circuit conditions, conductor insulation temperature rating, terminal rating, adjustment factor, correction factor, current-carrying conductor count, and the requirements enforced by the AHJ.

The calculation also does not determine whether a measured slip value is acceptable for a particular motor. Actual motor behavior depends on load, motor design, rotor condition, supply voltage, commanded VFD frequency, drive control method, and manufacturer operating data.

Use the calculated Slip frequency as a frequency conversion for motor and drive analysis. Verify actual operating values with appropriate measurements and the motor or drive manufacturer’s documentation when evaluating performance or troubleshooting.