Motor Synchronous Speed Calculator
Choose a mode and enter your own supply frequency and motor pole count. Poles are the total count, not pole pairs.
Choose a mode and enter your own supply frequency and motor pole count. Poles are the total count, not pole pairs.
AC induction-motor arithmetic: ns = 120f/p, Δn = ns − rpm, s = Δn/ns, rotor electrical frequency = sf. Negative slip represents generator operation; its signed frequency is an algebraic result and |sf| is the slip-frequency magnitude. No result is clamped.
DOE describes a load estimate, not precise measurement or fault diagnosis. Nameplate full-load slip can have a 20% reporting tolerance and speeds are often rounded to 5 rpm; measurement and voltage errors affect the estimate. This tool gives no safety rating or equipment-selection recommendation. Inputs and reports stay in this browser; nothing is uploaded or stored.
DOE — Estimate loadA QUICK WALKTHROUGH
How to use this tool
- Select speed/slip, pole comparison, or load estimation.
- Enter frequency and total poles; supply only the fields for your mode.
- Calculate, review assumptions, and copy or download the complete report.
Formula and scope
AC induction-motor arithmetic: ns = 120f/p, Δn = ns − rpm, s = Δn/ns, rotor electrical frequency = sf. Negative slip represents generator operation; its signed frequency is an algebraic result and |sf| is the slip-frequency magnitude. No result is clamped.
Estimate load
DOE slip-load estimate at rated supply frequency: 100(ns − measured rpm)/(ns − nameplate full-load rpm). Plain mode assumes rated voltage. Optional correction uses denominator |(ns − nameplate rpm)(rated V/measured V)²|. Compare measurements and nameplate data at the same rated frequency. Negative or above-100% results remain signed estimates; proportional slip is not physically linear over every operating condition.
Mode / assumptions
DOE describes a load estimate, not precise measurement or fault diagnosis. Nameplate full-load slip can have a 20% reporting tolerance and speeds are often rounded to 5 rpm; measurement and voltage errors affect the estimate. This tool gives no safety rating or equipment-selection recommendation. Inputs and reports stay in this browser; nothing is uploaded or stored. DOE: https://www.energy.gov/sites/prod/files/2014/04/f15/amo_motors_guidebook_web.pdf
GOOD TO KNOW
Common questions
Are poles the same as pole pairs?
No. Enter the total positive even pole count; four poles means two pole pairs.
Why is slip or load negative?
Speed above synchronous speed gives negative slip and a negative algebraic load estimate. This may describe generator operation; it is not a diagnosis.
Can I measure motor load precisely?
No. The DOE slip method is an estimate affected by nameplate tolerance, rounding, supply conditions and speed measurement.