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Motor Torque Speed Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Based on IEEE 112 and NEMA MG 1 motor standards. Last verified 14 June 2026.

This calculator solves the fundamental motor power-torque-speed relationship in both directions: calculate torque from known power and speed, or calculate power from known torque and speed. It also converts between common power units (kW and hp) and speed units (RPM and rad/s), and computes the full load current estimate for a three-phase induction motor.

Select which quantity to calculate
Rated shaft power output. 1 hp = 0.7457 kW.
Actual rotor speed at rated load (from nameplate)
-- rad/s
-- N.m
-- kW
-- hp

Motor power-torque-speed formulas

omega = 2 × pi × N / 60 (rad/s)
T = P / omega = 9,550 × PkW / NRPM (N.m)
P = T × omega (W)
Php = PkW / 0.7457

Where: T = torque (N.m), P = shaft power (W), omega = angular velocity (rad/s), N = speed (RPM), and 9,550 = 60,000 / (2 * pi) is a convenient constant for the kW/RPM/N.m combination.

Synchronous speeds at 50 Hz and 60 Hz

  • 2-pole: 3,000 RPM (50 Hz) or 3,600 RPM (60 Hz)
  • 4-pole: 1,500 RPM (50 Hz) or 1,800 RPM (60 Hz)
  • 6-pole: 1,000 RPM (50 Hz) or 1,200 RPM (60 Hz)
  • 8-pole: 750 RPM (50 Hz) or 900 RPM (60 Hz)
  • Actual rotor speed is synchronous speed minus slip (typically 2 to 5% for standard motors).

Motor torque and speed calculator: frequently asked questions

What is the relationship between torque, power, and speed?

Power (W) = Torque (N.m) * Angular velocity (rad/s). Angular velocity omega = 2 * pi * N / 60, where N is rotational speed in RPM. Therefore Torque (N.m) = Power (W) * 60 / (2 * pi * N). For example, a 15 kW motor at 1,450 RPM produces 15,000 * 60 / (2 * pi * 1,450) = 98.8 N.m of torque.

How do I convert between kW and horsepower?

1 mechanical horsepower (hp) = 745.7 watts (W). Therefore: Power (kW) = Power (hp) * 0.7457. For example, a 20 hp motor = 20 * 0.7457 = 14.91 kW. NEMA motor nameplates typically list power in horsepower; IEC motors use kilowatts.

What is full load torque?

Full load torque (FLT) is the torque a motor produces when running at rated power and rated speed. FLT (N.m) = 9,550 * P (kW) / N (RPM). The factor 9,550 = 60,000 / (2 * pi). For a 15 kW, 4-pole motor at 1,450 RPM: FLT = 9,550 * 15 / 1,450 = 98.8 N.m.

What is slip in an induction motor?

Slip is the difference between synchronous speed and actual rotor speed, expressed as a percentage. Slip (%) = (Ns - N) / Ns * 100, where Ns is synchronous speed = 120 * f / p (f = supply frequency, p = number of poles). A 4-pole motor at 50 Hz has Ns = 1,500 RPM. At 1,450 RPM actual speed, slip = (1500-1450)/1500 * 100 = 3.33%.

What is the difference between shaft torque and starting torque?

Shaft (running) torque is the torque at rated load and speed. Starting torque (locked rotor torque) is typically 150% to 300% of full load torque for standard NEMA Design B induction motors. Peak (breakdown) torque is typically 200% to 300% of full load torque. Motor selection must consider both the continuous load torque and the starting torque requirements.

Official sources

  • IEEE 112 Standard Test Procedure for Polyphase Induction Motors and Generators: IEEE 112.
  • NEMA MG 1 Motors and Generators: NEMA MG 1.

Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.