Electric Motor Torque Calculator for kW, HP and RPM
Calculate motor torque, power, or speed with kW/RPM or HP/RPM formulas, including Nm and ft·lb unit conversions.
Choose which variable to solve, pick your power and torque units, and enter the two known motor values to get the third instantly.
Electric Motor Torque Calculator for kW, HP and RPM
Calculate motor torque, power, or speed with kW/RPM or HP/RPM formulas, including Nm and ft·lb unit conversions.
Use power and speed to calculate motor torque.
About the electric motor torque calculator
Electric motor sizing always comes back to the relationship between power, torque, and rotational speed. This calculator uses the two common engineering shortcuts for that relationship. In metric form, torque in newton-meters is T = (P × 9549.3) / n when power is entered in kilowatts and speed is in revolutions per minute. In imperial form, torque in pound-feet is T = (HP × 5252) / RPM when power is in horsepower. These constants simply package the unit conversions that come from the more fundamental power equation P = Tω.
When you know power and speed, torque tells you how much twisting force the motor can deliver at the shaft. That number matters for conveyors, pumps, compressors, gearboxes, hoists, machine tools, and any other rotating load that must overcome inertia or resistive force. A motor with high speed but low torque may not start a heavy load reliably, while a lower-speed motor with more torque may perform much better in the same application. The calculator helps you see that tradeoff immediately.
The reverse calculations are just as useful. If you already know the required torque and intended operating speed, solving for power lets you estimate the motor size needed for the job. If you know the available power and required torque, solving for speed reveals the shaft RPM you can expect before gearing. These quick relationships are widely used during concept design, troubleshooting, and specification review because they provide a fast first-pass answer without requiring a full motor model.
Unit handling is often where mistakes happen. Many catalogs list motor output in kilowatts, but older equipment data sheets may use horsepower. Torque can likewise appear in Nm or ft·lb depending on industry and region. This calculator keeps the selected power unit tied to the proper constant and also shows converted values, so you can compare a metric motor spec against an imperial service manual without reworking the math by hand.
Remember that these formulas describe mechanical output at the shaft, not electrical input at the terminals. Real motor selection must still account for efficiency, service factor, starting current, gearbox losses, duty cycle, temperature rise, and transient load conditions. Even with those caveats, the speed-power-torque triangle remains one of the most practical checks a designer or technician can make, and it is exactly what this calculator is built to streamline.
Electric motor torque examples
Use these sample cases to sanity-check motor specifications in either metric or imperial units.
| Inputs | Output | Application note |
|---|---|---|
| Mode: Torque; P = 15 kW, n = 1450 RPM | T = 98.786897 Nm | A common industrial induction motor delivers just under 99 Nm at full-load speed. |
| Mode: Torque; P = 10 HP, n = 1750 RPM | T = 30.011429 ft·lb | This is a typical imperial motor rating used in pumps and blowers. |
| Mode: Speed; P = 5 kW, T = 20 Nm | n = 2387.325 RPM | If shaft torque demand is modest, a 5 kW machine can run at a comparatively high speed. |
How to use the electric motor torque calculator
- Choose whether you want to solve for torque, power, or speed.
- Pick the power unit and torque unit that match your motor data sheet or design notes.
- Enter the two known values for the selected mode, such as power and speed or torque and speed.
- Click Calculate to see the solved value plus converted power and torque in the alternate units.
Electric motor torque calculator FAQ
Why does the calculator use 9549.3 for kW and 5252 for HP?
Those constants come from combining the basic power equation with the unit conversions between angular speed, revolutions per minute, and torque. They let you use practical engineering units directly without converting everything to radians per second by hand.
What is the difference between torque and power?
Torque is the twisting force the motor delivers at the shaft, while power measures how quickly that torque is doing mechanical work. Two motors can have the same power but very different torque if they operate at different speeds.
Can I mix kW with ft·lb or HP with Nm?
Yes. The calculator converts torque to the proper internal unit for the selected power basis and then converts the result back to the torque unit you chose. That makes it useful when specifications come from different regions or suppliers.
Does this give electrical input power or shaft output power?
These formulas describe mechanical shaft output, which is what torque and rotational speed determine. Electrical input power will be higher than shaft output because real motors have efficiency losses.
Why might the calculated value differ from a nameplate?
A nameplate usually reflects rated operating conditions, nominal efficiency, slip, and manufacturer rounding. Real systems may also include gearbox losses, overload allowances, or non-steady operating points that are not represented in the simple formula.