06 — Tools
Torque from power and speed
The shortest useful formula in drive engineering: torque follows from power and speed. You need it for every gearbox selection and every check whether a motor will start the machine at all.
Result
- Torque
- —Nm
- Angular velocity
- —rad/s
Please fill all fields with valid numbers.
A guide, not a design to standard. The applicable standards and case-by-case verification govern.
Worked example
The default case the calculator starts with, worked through once. Change the values above and it recalculates immediately.
Inputs
- Shaft power
- 7.5 kW
- Speed
- 1,450 min⁻¹
Result
- Torque
- 49.4 Nm
- Angular velocity
- 152 rad/s
Formula
- M = 9550 · P / n (P in kW, n in min⁻¹, M in Nm)
- ω = 2π · n / 60
Assumptions and standards
- The constant 9550 comes from 60,000 / 2π and applies to power in kilowatts and speed in revolutions per minute.
- The result is rated torque at the operating point. Starting, pull-up and breakdown torque differ considerably and are given in the motor data sheet.
Frequently asked
Does the formula apply to geared motors?
Yes, if you enter the output speed. Output torque rises with the gear ratio, less the gearbox efficiency.
Why is rated torque not enough for sizing?
Because the critical point is usually starting. A machine with high breakaway torque needs a multiple of rated torque – starting torque governs there, not the value calculated here.
Calculating is the easy part.
A formula gives you a number. Designing a plant also demands installation method, grouping, discrimination, the standards in force and a look at the installed base. That is what we take on.
Contact
Tell us what it is about.
A phone call or three lines is enough. From the very start you talk to the people who will later work on your project – not to a distribution list.
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