Motor Shaft Torque Calculator
Shaft torque from motor power and speed. 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 shaft torque from shaft power and rated speed. 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
Use the nameplate speed (for example 1480 rpm), not 1500 rpm, or the torque will be understated.
Cross-check: 10 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 | 10 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 |
|---|---|
| Shaft power | 75 kW |
| Rated speed | 1,480 rpm |
- ω = 2π × N / 60 = 154.985 rad/s
- T = P / ω = 75,000 / 154.985 = 483.92 N·m
Assumptions
- Power is mechanical shaft output
- Speed is the loaded rotor speed, not synchronous speed
Use the nameplate speed (for example 1480 rpm), not 1500 rpm, or the torque will be understated.
Inputs and results
| Input | Unit | Allowed or shown | Note |
|---|---|---|---|
| Shaft power | kW | greater than 0 kW | |
| Rated speed | rpm | greater than 0 rpm |
| Result | Unit | Allowed or shown | Note |
|---|---|---|---|
| Shaft torque | N·m | Shown to 1 decimal place |
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 shaft power
| Shaft power (kW) | Shaft torque (N·m) |
|---|---|
| 7.5 | 48.4 |
| 18.8 | 121.3 |
| 37.5 | 242 |
| 75 | 483.9 |
| 150 | 967.8 |
| 300 | 1,935.7 |
| 750 | 4,839.2 |
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 shaft power and rated speed. Change the unit of a value with its selector and the result stays the same.
What does this calculator assume?
Power is mechanical shaft output. Speed is the loaded rotor speed, not synchronous speed.
Which calculators should I use next?
Common next steps are Induction Motor Slip and Motor Starting Current. 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. 10 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.
- Induction Motor Formulas: Induction motor formulas for synchronous speed, slip, shaft torque and full-load current
- Synchronous Speed and Pole Formulas: Synchronous speed formulas: the speed of a rotating field from the frequency and the poles
- Gear and Belt Drive Formulas: Speed and Torque: Gear and belt drive formulas: speed ratio from teeth or pulley diameters, output speed, torque and power with efficiency
- Hoist and Lift Power Formulas: Hoist formulas: the motor power to raise a load at a speed, the energy to lift it a height and the lifting time
- Conveyor Belt Power Formulas: Belt conveyor power formulas: the material load per metre, the friction force
More Motor Engineering calculatorsAll engineering calculatorsMotor Shaft Torque in Elecmetric