Electric Motor Torque Calculator — Power, Speed & Torque
Enter an electric motor's rated shaft power, speed in RPM and efficiency to get shaft torque, angular velocity and — optionally — the three-phase full-load current. Useful for motor selection, coupling sizing and drive specification.
kW
RPM
%
V
Mechanical torque at the rated shaft speed
- 1
Shaft power in watts
3 × 1000 = 3,000 - 2
Angular velocity ω = 2π × N ÷ 60
2π × 1,500 ÷ 60 = 157.0796Converts shaft speed from RPM to radians per second. - 3
Shaft torque T = P ÷ ω
3,000 ÷ 157.0796 = 19.10
How does this calculator work?
Shaft torque T = P / ω where ω = 2πN/60. A motor rated at P kW at N RPM delivers T = 9549 × P / N (N·m) at the shaft. Input power = shaft power / efficiency; three-phase full-load current ≈ P_in / (√3 × V_line). Results are at rated steady-state — starting and peak torques can be 2–3 times higher.
Formula
How this is calculated
The fundamental relationship between mechanical power, torque and rotational speed is P = T × ω, where ω is the angular velocity in radians per second. Converting shaft speed from RPM: ω = 2π N / 60. Rearranging gives the shaft torque T = P / ω. This is the torque available at the motor's output shaft — the torque the motor actually delivers to the load.
The mechanical output power is always less than the electrical input power because of losses (copper losses in the windings, iron losses in the core, friction and windage). The efficiency η = P_shaft / P_input, so P_input = P_shaft / η. For a three-phase motor operating at unity power factor, the full-load phase current is approximately I = P_input / (√3 × V_line). Real motors have power factors of 0.80–0.95, so the actual current drawn will be slightly higher than this estimate — use it as a guide rather than a precise design figure.
The calculation assumes steady-state (rated) operation. Starting torque, peak torque and transient currents at start-up can be several times the rated values shown here.
Frequently asked questions
Use T (N·m) = P (W) / ω (rad/s), where ω = 2π × RPM / 60. Equivalently, T = 9549 × P (kW) / N (RPM). A 3 kW motor running at 1500 RPM produces 19.1 N·m.
Every motor has losses — heat in the windings (copper losses), eddy currents in the core (iron losses), and mechanical friction. Efficiency η accounts for all of these; a 90 % efficient motor needs 10 % more electrical power than it delivers mechanically.
No — it assumes unity power factor. Real AC induction motors have power factors of 0.80–0.95 at full load, so the actual current drawn will be 5–25 % higher. Use the estimate for initial sizing only and verify with the motor nameplate.
Also known as
TG we-Calculate Editorial Team. (2026). Electric Motor Torque Calculator — Power, Speed & Torque [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/electric-motor-torque-calculator
TG we-Calculate Editorial Team. "Electric Motor Torque Calculator — Power, Speed & Torque." TG we-Calculate. 2026. https://we-calculate.com/calculator/electric-motor-torque-calculator.
TG we-Calculate Editorial Team, "Electric Motor Torque Calculator — Power, Speed & Torque," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/electric-motor-torque-calculator
@misc{wecalculate_electric_motor_torque_calculator, title = {Electric Motor Torque Calculator — Power, Speed & Torque}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/electric-motor-torque-calculator}}, year = {2026}, note = {TG we-Calculate} }
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