Please enter valid positive numeric values for power and speed. Speed cannot be zero.
Calculated Rated Torque
Torque (Newton-meters):–
Torque (Foot-pounds):–
function calculateMotorTorque() {
// Get input values
var powerInput = document.getElementById('motorPower').value;
var powerUnit = document.getElementById('powerUnit').value;
var speedInput = document.getElementById('motorSpeed').value;
var resultDiv = document.getElementById('torqueResult');
var errorDiv = document.getElementById('calcError');
// Parse inputs
var power = parseFloat(powerInput);
var speed = parseFloat(speedInput);
// Validate inputs
if (isNaN(power) || isNaN(speed) || power <= 0 || speed <= 0) {
errorDiv.style.display = 'block';
resultDiv.style.display = 'none';
return;
}
// Clear previous errors
errorDiv.style.display = 'none';
var torqueNm = 0;
var torqueFtLb = 0;
// Constants for calculation based on standard engineering formulas
var constantSI = 9550; // For kW and RPM to get Nm
var constantImperial = 5252; // For HP and RPM to get ft-lb
var nmToFtlbFactor = 0.737562; // Conversion factor
if (powerUnit === 'kW') {
// Calculate in Nm first: T = (9550 * P_kW) / N_rpm
torqueNm = (constantSI * power) / speed;
// Convert to ft-lb
torqueFtLb = torqueNm * nmToFtlbFactor;
} else {
// Unit is HP
// Calculate in ft-lb first: T = (5252 * P_hp) / N_rpm
torqueFtLb = (constantImperial * power) / speed;
// Convert to Nm
torqueNm = torqueFtLb / nmToFtlbFactor;
}
// Display results formatted to 2 decimal places
document.getElementById('resultNm').textContent = torqueNm.toFixed(2) + " Nm";
document.getElementById('resultFtLb').textContent = torqueFtLb.toFixed(2) + " ft-lb";
resultDiv.style.display = 'block';
}
Understanding Rated Torque in Induction Motors
Rated torque is a critical parameter in electrical engineering and mechanical design. It represents the rotational force an induction motor is designed to provide continuously at its rated output power and rated speed without overheating. Correctly determining this value is essential for selecting the right motor for a specific load application, whether it's driving a conveyor belt, a pump, or an industrial fan.
The Physics Behind the Calculation
The relationship between power, torque, and rotational speed is fundamental to rotational mechanics. Power is essentially the rate at which torque performs work. The basic formula relating these three variables is:
Power (P) = Torque (τ) × Angular Velocity (ω)
However, in practical industrial applications, angular velocity is rarely expressed in radians per second. Instead, we use Revolutions Per Minute (RPM), and power is expressed in either Kilowatts (kW) or Horsepower (HP). To accommodate these practical units, standard engineering constants are introduced into the formula.
Formulas Used in This Calculator
Depending on the unit of power available from the motor nameplate, one of two derived formulas is used to calculate the rated torque.
1. Using International System (SI) Units (kW and Nm)
If the rated power is given in Kilowatts (kW), the rated torque in Newton-meters (Nm) is calculated using the constant 9550:
Torque (Nm) = (9550 × Power in kW) / Speed in RPM
2. Using Imperial Units (HP and ft-lb)
If the rated power is given in Horsepower (HP), the rated torque in foot-pounds (ft-lb) is calculated using the constant 5252:
Torque (ft-lb) = (5252 × Power in HP) / Speed in RPM
How to Use the Calculator
To find the rated torque of your motor, locate the motor nameplate and input the following data into the calculator above:
Rated Power: Enter the numerical value of the motor's power output. Be sure to select the correct unit (kW or HP) from the dropdown menu next to the input field.
Rated Speed (RPM): Enter the full-load speed of the motor in revolutions per minute. Do not use the synchronous speed (e.g., use 1450 RPM, not 1500 RPM for a 4-pole 50Hz motor), as rated torque occurs at the rated slip speed.
The calculator will instantly provide the full-load torque in both Newton-meters and foot-pounds, allowing you to verify if the motor is suitably sized for the required mechanical load.