Motor Output Power and Loss Calculator
Shaft power and losses from measured voltage, current, power factor and efficiency. With the formula, a worked example and typical values.
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Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
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About this calculator
This page calculates electrical input, shaft output and motor loss from line voltage, line current, power factor and efficiency. Change any value or its unit and the result updates. The steps below show the working for the default values, so you can check each line against your own method.
Limits of this calculator
Change the shaft output unit to HP. Motors lose efficiency below about 50% load.
Cross-check: 6 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review.
Verification status: Engineering reference
Engineering reference. Formula and method documented and tested against separately coded reference calculations. Not yet Verified: the evidence listed on this page is still needed.
What this calculator checks
- The arithmetic of the published formula for the values you entered, in the units shown.
What remains unverified
- That the inputs suit your application. Take ratings, resistances and constants from the manufacturer data sheet or project specification.
Verification register entry
| Calculation author | Rahul Sharma (author) |
|---|---|
| Technical review | No independent technical review has been carried out |
| Individual professional approval | Not recorded |
| Formula reference | not recorded |
| Standard and edition | Not applicable: Textbook machine relation (slip, torque, shaft power, transformer efficiency); inputs come from the data sheet |
| Standard review state | Not applicable |
| Scope-screening note | not recorded |
| Cross-check test cases | 6 reference vectors (tests/reference_vectors.json) |
| Review date | not recorded |
| Next review date | not recorded |
| Status | Engineering reference |
Needed before this calculator can be marked Verified: reviewer name, qualification and review date; exact formula reference; formula source (textbook or standard); next review date.
Formula
Worked example
| Input | Value |
|---|---|
| Line voltage (L-L) | 415 V |
| Line current | 140 A |
| Power factor | 0.88 |
| Efficiency | 0.93 |
- Pin = √3 × 415 × 140 × 0.88 = 88.556 kW
- Pout = 88.556 × 0.93 = 82.357 kW = 110.44 HP
Assumptions
- Three-phase, balanced
- Efficiency is the value at this load, not nameplate
Change the shaft output unit to HP. Motors lose efficiency below about 50% load.
Inputs and results
| Input | Unit | Allowed or shown | Note |
|---|---|---|---|
| Line voltage (L-L) | V | greater than 0 V | |
| Line current | A | greater than 0 A | |
| Power factor | (number) | greater than 0, up to 1 | Rough starting point only. Resistive heating and incandescent loads are 1.0; a fully loaded induction motor is typically 0.8 to 0.88 and falls sharply when lightly loaded; discharge lighting depends on its ballast or driver. For real work use the nameplate or a measured value. |
| Efficiency | (number) | greater than 0, up to 1 |
| Result | Unit | Allowed or shown | Note |
|---|---|---|---|
| Electrical input | kW | Shown to 2 decimal places | |
| Shaft output | kW | Shown to 2 decimal places | |
| Motor loss | kW | Shown to 2 decimal places |
How it is calculated
Each input is converted to the base unit of its quantity, the formula above is applied in the order shown in the worked example, and each result is shown in the unit you choose. Results are held at full precision and rounded only for display, except where a step selects a standard size, as the worked example shows. A value outside its allowed range is refused with a message instead of giving a result.
How the result changes with line voltage (l-l)
| Line voltage (L-L) (V) | Electrical input (kW) | Shaft output (kW) | Motor loss (kW) |
|---|---|---|---|
| 41.5 | 8.86 | 8.24 | 0.62 |
| 104 | 22.19 | 20.64 | 1.55 |
| 208 | 44.38 | 41.28 | 3.11 |
| 415 | 88.56 | 82.36 | 6.2 |
| 830 | 177.11 | 164.71 | 12.4 |
| 1,660 | 354.23 | 329.43 | 24.8 |
| 4,150 | 885.56 | 823.57 | 61.99 |
Other inputs are the same as in the worked example above.
Standards and further reading
- IEC 60034-1 (rotating electrical machines, rating and performance)
- IEC 60034-30-1 (efficiency classes)
Where the motor nameplate or data sheet gives a value, use it in place of a calculated one. These are named as background reading. Elecmetric does not embed clause text or rating tables, and the reviewer record for this calculator is separate from this list.
Frequently asked questions
What do I need to enter?
Enter line voltage (L-L), line current, power factor and efficiency. Change the unit of a value with its selector and the result stays the same.
What does this calculator assume?
Three-phase, balanced. Efficiency is the value at this load, not nameplate.
Which calculators should I use next?
Common next steps are Motor Full-Load Current and Motor Shaft Torque. The related links at the bottom of this page open them.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. 6 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review. Check design values against the standard and the equipment data you work to.
Formula guides and reference
Longer explanations with worked examples and tables, written for the same topic.
- Motor Efficiency Formulas: Input and Savings: Motor efficiency formulas: input power and losses from shaft power
- Induction Motor Formulas: Induction motor formulas for synchronous speed, slip, shaft torque and full-load current
- Motor Temperature Rise Formulas: Motor winding temperature formulas: the hot temperature from the change in resistance
More Motor Engineering calculatorsAll engineering calculatorsMotor Output Power and Efficiency Loss in Elecmetric