# Motor Efficiency Calculator (η = P_out / P_in)

Compute motor efficiency η = P_out / P_in. Supports electrical input (single-phase U·I·cosφ or three-phase √3·U·I·cosφ) or direct P_in; output power can be derived from a loss breakdown (copper+iron+rotor copper+mechanical+stray) or supplied directly.

> Canonical page: https://elysiatools.com/en/tools/motor-efficiency-calculator

- **Category:** Math & Numbers

- **Keywords:** motor efficiency, efficiency, P_out / P_in, electrical input power, three-phase power, loss breakdown, copper loss, iron loss, motor losses, electrical engineering

## Overview

The Motor Efficiency Calculator computes electric motor efficiency (η = P_out / P_in) using either direct power values or electrical parameters. It supports single-phase and three-phase electrical inputs, and can calculate output power directly or derive it by subtracting stator copper, iron, rotor copper, mechanical, and stray load losses from the input power.

## Inputs

- **Power Input Mode** (select)
- **Phase** (select): Only used in Electrical mode.
- **Voltage U (V)** (number): Required in Electrical mode. Line-to-line voltage for three-phase.
- **Current I (A)** (number): Required in Electrical mode. Line current.
- **Power Factor cosφ** (number): Required in Electrical mode. 0 < cosφ ≤ 1.
- **Input Power P_in (W)** (number): Required in Direct mode. Total electrical input power in watts.
- **Use Loss Breakdown** (checkbox): If checked, P_out is derived from the loss breakdown below instead of the explicit P_out field.
- **Output Power P_out (W)** (number): Required when Use Loss Breakdown is off. Shaft mechanical output power in watts.
- **Stator Copper Loss P_cu1 (W)** (number): Used when Use Loss Breakdown is on.
- **Iron Loss P_fe (W)** (number): Core (iron) loss. Used when Use Loss Breakdown is on.
- **Rotor Copper Loss P_cu2 (W)** (number): Used when Use Loss Breakdown is on.
- **Mechanical Loss P_mech (W)** (number): Friction + windage. Used when Use Loss Breakdown is on.
- **Stray Load Loss P_stray (W)** (number): Additional (stray-load) losses. Used when Use Loss Breakdown is on.
- **Decimal Places** (number)

## When to use

- When evaluating the performance of single-phase or three-phase electric motors using measured voltage, current, and power factor.
- When calculating motor efficiency using a detailed loss breakdown, including copper, iron, mechanical, and stray load losses.
- When verifying manufacturer-specified efficiency ratings against real-world input and output power measurements.

## How it works

- Select the power input mode: choose 'Electrical' to calculate input power from voltage, current, and power factor, or 'Direct' to enter input power in watts.
- Specify the output power method: enter the shaft output power directly, or enable the loss breakdown to subtract stator copper, iron, rotor copper, mechanical, and stray losses from the input power.
- Click calculate to compute the total input power, total losses, shaft output power, and the final motor efficiency percentage.

## Use cases

- Determining the efficiency of an industrial three-phase induction motor using field measurements of voltage, current, and power factor.
- Analyzing energy losses in a motor prototype by inputting stator copper, rotor copper, iron, mechanical, and stray losses.
- Comparing the efficiency of different motor operating points during commissioning or energy audits.

## Frequently asked questions

### How does the calculator compute input power in three-phase mode?

It uses the formula P_in = √3 × U × I × cosφ, where U is line-to-line voltage, I is line current, and cosφ is the power factor.

### What losses are included in the loss breakdown option?

It accounts for stator copper loss, iron (core) loss, rotor copper loss, mechanical (friction and windage) loss, and stray load loss.

### Can I calculate efficiency if I only know the direct input and output power?

Yes, set the input mode to 'Direct' and disable the loss breakdown to enter P_in and P_out directly.

### What is the difference between single-phase and three-phase electrical modes?

Single-phase uses P_in = U × I × cosφ, while three-phase incorporates the √3 multiplier for line-to-line calculations.

### What unit should be used for power inputs and losses?

All power inputs, output power, and individual losses must be entered in Watts (W).

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