Motor Torque Calculator
Calculate motor torque from power and speed (or vice versa). Convert between Newton-meters (N·m), pound-feet (lb·ft), and kilogram-meters (kg·m). Supports DC, single-phase, and three-phase motors.
What Is Motor Torque?
Motor torque is the rotational force produced by an electric motor. It is measured in Newton-meters (N·m), pound-feet (lb·ft), or kilogram-meters (kg·m). Torque is a fundamental parameter for selecting and sizing motors for mechanical applications.
The relationship between torque, power, and speed is:
T (N·m) = (P (kW) × 9549) / RPM
T (lb·ft) = (HP × 5252) / RPM
T (kg·m) = (P (kW) × 974) / RPM
Where:
- P = Mechanical power output
- RPM = Rotational speed
- T = Torque
This calculator also shows the electrical input power required to achieve the mechanical output, considering motor efficiency and power factor for AC motors.
How Does the Motor Torque Calculator Work?
The calculator supports two modes:
- Torque from Power: Enter power and speed to calculate torque. The calculator also determines the electrical input power required based on efficiency and power factor.
- Power from Torque: Enter torque and speed to calculate power. The calculator also determines the electrical input power required based on efficiency and power factor.
The formulas used are:
From Power to Torque:
T (N·m) = (P (kW) × 9549) / RPM
T (lb·ft) = (HP × 5252) / RPM
T (kg·m) = (P (kW) × 974) / RPM
From Torque to Power:
P (kW) = (T (N·m) × RPM) / 9549
HP = (T (lb·ft) × RPM) / 5252
For AC motors, the electrical input power is calculated using:
- Single-Phase: Pin = V × I × PF
- Three-Phase: Pin = √3 × V × I × PF
The mechanical output power is Pout = Pin × η, where η is the efficiency.
Why Use This Motor Torque Calculator?
- Three Motor Types: Supports DC, Single-Phase AC, and Three-Phase AC motors.
- Two Calculation Modes: Calculate torque from power or power from torque.
- Multiple Units: Convert between N·m, lb·ft, and kg·m for torque, and kW, HP, and W for power.
- Efficiency & Power Factor: Includes motor efficiency and power factor for accurate electrical input power calculations.
- Formula Display: See the formula used for each calculation.
- Free & Private: No registration, no data storage.
❓ Motor Torque Calculator FAQ
What is motor torque?
Motor torque is the rotational force produced by an electric motor. It is measured in Newton-meters (N·m), pound-feet (lb·ft), or kilogram-meters (kg·m).
How do I calculate torque from power and speed?
Use the formula: T (N·m) = (P (kW) × 9549) / RPM. For HP: T (lb·ft) = (HP × 5252) / RPM.
How do I calculate power from torque and speed?
Use the formula: P (kW) = (T (N·m) × RPM) / 9549. For HP: HP = (T (lb·ft) × RPM) / 5252.
What is the difference between N·m, lb·ft, and kg·m?
N·m (Newton-meter) is the SI unit of torque. lb·ft (pound-foot) is the imperial unit. kg·m (kilogram-meter) is another metric unit. 1 N·m = 0.73756 lb·ft = 0.101972 kg·m.
What is the relationship between torque and horsepower?
Horsepower = (Torque × RPM) / 5252 (for lb·ft). This means at 5252 RPM, torque and horsepower are numerically equal.
What is motor efficiency and why does it matter?
Motor efficiency is the ratio of mechanical output power to electrical input power. It matters because it determines how much electrical power is needed to achieve a given mechanical output.
What is power factor in AC motors?
Power factor (PF) is the ratio of real power to apparent power in AC circuits. It represents how effectively electrical power is converted into useful work. A PF of 0.85-0.9 is typical for induction motors.
How do I convert kW to HP?
1 HP = 0.746 kW. To convert kW to HP, divide by 0.746. To convert HP to kW, multiply by 0.746.
What is the formula for three-phase motor power?
Pin = √3 × V × I × PF. This is the electrical input power. The mechanical output power is Pout = Pin × η.
What is the formula for single-phase motor power?
Pin = V × I × PF. The mechanical output power is Pout = Pin × η.
What is the formula for DC motor power?
Pin = V × I. The mechanical output power is Pout = Pin × η.
How do I calculate motor current from power?
For three-phase: I = P / (√3 × V × PF × η). For single-phase: I = P / (V × PF × η). For DC: I = P / (V × η).
What is a typical motor efficiency?
Typical efficiencies for motors under load are 85-95%. Smaller motors tend to have lower efficiency, while larger motors can achieve 96% or higher.
What is the difference between torque and horsepower?
Torque is a measure of rotational force, while horsepower is a measure of power (work done over time). The relationship is: HP = (Torque × RPM) / 5252.
What is the relationship between motor speed and torque?
For a given power output, torque is inversely proportional to speed. Higher speed means lower torque, and lower speed means higher torque.
How do I determine motor size for my application?
Calculate the required torque and speed for your application, then use this calculator to find the required power. Add a safety factor of 15-20% when selecting the motor.
What is the difference between starting torque and running torque?
Starting torque (or locked-rotor torque) is the torque produced when the motor is at standstill. Running torque is the torque produced at the motor's operating speed. Starting torque is typically higher than running torque.