Machines
Synchronous Speed Calculator
Estimate the rotating-field speed from frequency and the number of poles.
02 / Result
Synchronous speed
n = 120 × f / p
The synchronous speed will appear here.
Method, example and boundaries
Synchronous speed is n = 120 × f / p, with f in hertz and p the number of poles. A 60 Hz, 4-pole field runs at 120 × 60 / 4 = 1,800 rpm. A 50 Hz, 4-pole field runs at 1,500 rpm. The English page starts from the NEC preset of 60 Hz; IEC 50 Hz and the GB 50 Hz preset are selectable and do not change the equation.
This is the speed of the stator field, not the shaft speed of an induction motor and not a statement that a machine may be installed. Pole-changing windings, harmonics and converter pulse patterns are outside the model. Odd pole counts and frequencies above 400 Hz are rejected as outside this calculator’s domain.
Source: NEMA, Motor Terminology and Electrical Performance Characteristics (SRC-062), which states synchronous speed = 120 × frequency / poles and lists the 50 Hz and 60 Hz pole table. The specific NEMA clause number was not separately transcribed and is UNVERIFIED. No GB/T clause number is claimed for the 50 Hz preset; that preset reuses this site’s existing GB profile.
FAQ
What does this calculator compute?
Synchronous speed is n = 120 × f / p, with frequency in hertz and p the number of poles. A 60 Hz, 4-pole field is 1,800 rpm. A 50 Hz, 4-pole field is 1,500 rpm.
What do the frequency presets change?
The English page starts at the 60 Hz preset. The 50 Hz presets only fill the frequency field. They do not change the equation.
What is this speed not?
It is the stator-field speed, not the shaft speed of an induction motor, and not permission to install a machine. The NEMA clause number for the cited handout is UNVERIFIED. No GB/T clause number is claimed for the 50 Hz preset.
Source records
Motor Terminology and Electrical Performance Characteristics (SRC-062)
Institution: NEMA
Section: Training handout. Synchronous speed = 120 × frequency / poles. Not the text of NEMA MG 1.
URL on the calculation record: https://www.nema.org/docs/default-source/motor-and-generator-guides-and-resources-library/6-electric-motor-terminology-and-performance-characteristics-v2.pdf
Verification date: 2026-10-20
Status: review-required; NEMA MG 1 clause number UNVERIFIED
A GB/T 156 clause number for the 50 Hz preset is UNVERIFIED and is not invented on this page.