Calculate Synchronous Speed, Slip RPM, and Slip Percentage
2 Poles
4 Poles
6 Poles
8 Poles
10 Poles
12 Poles
Please enter valid numerical values.
Synchronous Speed (Ns):– RPM
Slip Speed:– RPM
Slip Percentage (s):– %
How to Calculate Slip Rate in Induction Motors
In electrical engineering, Slip is a fundamental concept for the operation of AC induction motors. It represents the difference between the rotating magnetic field's speed (Synchronous Speed) and the actual physical speed of the rotor (Rotor Speed). This relative motion is necessary to generate torque.
Understanding how to calculate slip rate is essential for diagnosing motor efficiency, loading conditions, and verifying nameplate data against real-world performance.
The Slip Formula
To calculate slip, you first need to determine the Synchronous Speed of the motor, which depends on the supply frequency and the number of magnetic poles.
For most standard NEMA Design B induction motors, the full-load slip typically ranges between 1.5% and 5%.
If the slip is 0%, the rotor is moving at the same speed as the magnetic field, meaning no torque is produced. If the slip is 100%, the rotor is stationary (locked rotor condition).
Use the calculator above to quickly verify if your motor is operating within its rated specifications based on your frequency and pole configuration.
function calculateMotorSlip() {
// 1. Get input values strictly by ID
var freqInput = document.getElementById("supplyFreq");
var polesInput = document.getElementById("numPoles");
var rotorInput = document.getElementById("rotorSpeed");
var errorDisplay = document.getElementById("errorMsg");
var resultsDisplay = document.getElementById("resultsDisplay");
// 2. Parse values
var f = parseFloat(freqInput.value);
var p = parseInt(polesInput.value);
var n = parseFloat(rotorInput.value);
// 3. Validation
if (isNaN(f) || isNaN(p) || isNaN(n) || f <= 0 || p <= 0) {
errorDisplay.style.display = "block";
resultsDisplay.style.display = "none";
return;
}
// Hide error if valid
errorDisplay.style.display = "none";
// 4. Calculate Synchronous Speed (Ns)
// Formula: 120 * Frequency / Poles
var syncSpeed = (120 * f) / p;
// 5. Calculate Slip Speed
// Formula: Sync Speed – Rotor Speed
var slipSpeed = syncSpeed – n;
// 6. Calculate Slip Percentage
// Formula: (Slip Speed / Sync Speed) * 100
var slipPercent = (slipSpeed / syncSpeed) * 100;
// 7. Update DOM with results
// Rounding for clean display
document.getElementById("resSyncSpeed").innerHTML = syncSpeed.toFixed(0) + " RPM";
document.getElementById("resSlipSpeed").innerHTML = slipSpeed.toFixed(0) + " RPM";
document.getElementById("resSlipPercent").innerHTML = slipPercent.toFixed(2) + "%";
// 8. Show Results
resultsDisplay.style.display = "block";
}