Induction Motor Slip Calculator
Synchronous speed and slip from frequency, poles and rotor speed. With the formula, a worked example and typical values.
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Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
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About this calculator
This page calculates synchronous speed and slip from supply frequency, number of poles and rotor speed. Change any value or its unit and the result updates. The steps below show the working for the default values, so you can check each line against your own method.
Limits of this calculator
Typical full-load slip is 1% to 5% for standard cage motors.
Cross-check: 6 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review.
Verification status: Engineering reference
Engineering reference. Formula and method documented and tested against separately coded reference calculations. Not yet Verified: the evidence listed on this page is still needed.
What this calculator checks
- The arithmetic of the published formula for the values you entered, in the units shown.
What remains unverified
- That the inputs suit your application. Take ratings, resistances and constants from the manufacturer data sheet or project specification.
Verification register entry
| Calculation author | Rahul Sharma (author) |
|---|---|
| Technical review | No independent technical review has been carried out |
| Individual professional approval | Not recorded |
| Formula reference | not recorded |
| Standard and edition | Not applicable: Textbook machine relation (slip, torque, shaft power, transformer efficiency); inputs come from the data sheet |
| Standard review state | Not applicable |
| Scope-screening note | not recorded |
| Cross-check test cases | 6 reference vectors (tests/reference_vectors.json) |
| Review date | not recorded |
| Next review date | not recorded |
| Status | Engineering reference |
Needed before this calculator can be marked Verified: reviewer name, qualification and review date; exact formula reference; formula source (textbook or standard); next review date.
Formula
Worked example
| Input | Value |
|---|---|
| Supply frequency | 50 Hz |
| Number of poles | 4 |
| Rotor speed | 1,470 rpm |
- Ns = 120 × 50 / 4 = 1,500 rpm
- slip = (1,500 − 1,470) / 1,500 × 100 = 2 %
Assumptions
- Motor operation (rotor at or below synchronous speed)
- Poles is the total pole count
Typical full-load slip is 1% to 5% for standard cage motors.
Inputs and results
| Input | Unit | Allowed or shown | Note |
|---|---|---|---|
| Supply frequency | Hz | greater than 0 Hz | |
| Number of poles | (number) | 2 or more, up to 48 | |
| Rotor speed | rpm | greater than 0 rpm |
| Result | Unit | Allowed or shown | Note |
|---|---|---|---|
| Synchronous speed | rpm | Shown to 0 decimal places | |
| Slip (%) | (number) | Shown to 2 decimal places |
How it is calculated
Each input is converted to the base unit of its quantity, the formula above is applied in the order shown in the worked example, and each result is shown in the unit you choose. Results are held at full precision and rounded only for display, except where a step selects a standard size, as the worked example shows. A value outside its allowed range is refused with a message instead of giving a result.
How the result changes with rotor speed
| Rotor speed (rpm) | Synchronous speed (rpm) | Slip |
|---|---|---|
| 1,000 | 1,500 | 33.33 |
| 1,200 | 1,500 | 20 |
| 1,400 | 1,500 | 6.67 |
| 1,470 | 1,500 | 2 |
| 1,480 | 1,500 | 1.33 |
| 1,490 | 1,500 | 0.67 |
| 1,499 | 1,500 | 0.07 |
Other inputs are the same as in the worked example above.
Standards and further reading
- IEC 60034-1 (rotating electrical machines, rating and performance)
- IEC 60034-30-1 (efficiency classes)
Where the motor nameplate or data sheet gives a value, use it in place of a calculated one. These are named as background reading. Elecmetric does not embed clause text or rating tables, and the reviewer record for this calculator is separate from this list.
Frequently asked questions
What do I need to enter?
Enter supply frequency, number of poles and rotor speed. Change the unit of a value with its selector and the result stays the same.
What does this calculator assume?
Motor operation (rotor at or below synchronous speed). Poles is the total pole count.
Which calculators should I use next?
Common next steps are Motor Shaft Torque and Motor Full-Load Current. The related links at the bottom of this page open them.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. 6 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review. Check design values against the standard and the equipment data you work to.
Formula guides and reference
Longer explanations with worked examples and tables, written for the same topic.
- Synchronous Speed and Pole Formulas: Synchronous speed formulas: the speed of a rotating field from the frequency and the poles
- Induction Motor Formulas: Induction motor formulas for synchronous speed, slip, shaft torque and full-load current
More Motor Engineering calculatorsAll engineering calculatorsInduction Motor Slip in Elecmetric