Motor Power Calculator
Calculate electric motor power, torque, current, and efficiency. Supports DC, single-phase, and three-phase motors. Enter any two known values to calculate the remaining parameters.
What Is Motor Power?
Motor power is the rate at which an electric motor converts electrical energy into mechanical energy. There are two key power measurements for motors:
- Electrical Input Power (Pin): The electrical power consumed by the motor from the supply. For AC motors, this includes power factor considerations.
- Mechanical Output Power (Pout): The usable mechanical power delivered at the motor shaft. This is always less than the input power due to losses.
The efficiency of a motor is the ratio of output power to input power: η = Pout / Pin. Typical motor efficiencies range from 85-95% for modern motors under load.
How Does the Motor Power Calculator Work?
The calculator uses standard motor power formulas:
DC Motor: Pin = V × I, Pout = Pin × η
Single-Phase AC: Pin = V × I × PF, Pout = Pin × η
Three-Phase AC: Pin = √3 × V × I × PF, Pout = Pin × η
Torque: Pout (kW) = (T × RPM) / 9549, or T (N·m) = (P × 9549) / RPM
The calculator supports two modes:
- Power & Current: Enter voltage, current, power factor (AC), and efficiency to calculate input power, output power, torque, and horsepower.
- Torque & Speed: Enter torque, speed, and efficiency to calculate output power, input power, current, and horsepower.
Why Use This Motor Power Calculator?
- Three Motor Types: Supports DC, Single-Phase AC, and Three-Phase AC motors.
- Two Calculation Modes: Calculate from power/current or torque/speed.
- Comprehensive Results: Get input power, output power, torque, current, horsepower, and efficiency.
- Formula Display: See the formula used for each calculation.
- Free & Private: No registration, no data storage.
❓ Motor Power Calculator FAQ
What is the difference between electrical input power and mechanical output power?
Electrical input power is the power consumed from the supply. Mechanical output power is the usable power delivered at the motor shaft. The difference is lost as heat and other losses.
What is motor efficiency?
Motor efficiency is the ratio of mechanical output power to electrical input power, expressed as a percentage. η = Pout / Pin × 100%.
What is power factor and why does it matter?
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 calculate motor torque from power and speed?
Torque (N·m) = (Power (kW) × 9549) / Speed (RPM). For horsepower: Torque (lb·ft) = (HP × 5252) / RPM.
What is the formula for three-phase motor power?
Pin = √3 × V × I × PF. Pout = Pin × η.
What is the formula for single-phase motor power?
Pin = V × I × PF. Pout = Pin × η.
What is the formula for DC motor power?
Pin = V × I. Pout = Pin × η.
How do I convert kW to horsepower?
1 HP = 0.746 kW. To convert kW to HP, divide by 0.746. To convert HP to kW, multiply by 0.746.
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.
How do I measure motor current?
Use a clamp meter to measure the current in one of the supply lines. For three-phase motors, measure the current in each phase and use the average value.
What is the relationship between motor speed and frequency?
For AC induction motors, speed is proportional to frequency: Speed (RPM) = (120 × Frequency) / Number of Poles. This is the synchronous speed; actual speed is slightly lower due to slip.
Can I use this calculator for VFD-fed motors?
This calculator provides estimates for VFD-fed motors, but accuracy may be affected by harmonics. For precise calculations, consider using specialized VFD analysis tools.
What is the difference between kW and kVA?
kW is real power (useful work), while kVA is apparent power (total power including reactive power). The relationship is: kW = kVA × PF.
How do I determine motor size without a nameplate?
Measure voltage and current under load, estimate power factor (0.85 for three-phase induction motors), and efficiency (90% for motors >5 HP). Then use this calculator to estimate output power.
What is the formula for motor torque in N·m?
Torque (N·m) = (Power (W) × 60) / (2π × RPM). Alternatively, T (N·m) = (P (kW) × 9549) / RPM.