Did you know how to calculate coupling sizing
22 Sep, 2021

How to calculate coupling sizing

The two ways to calculate coupling sizing are:

Fundamentals of Calculating Coupling Sizing Torque

One key component of sizing and selecting nearly every coupling is calculating the Nominal Torque as well as the Design Torque. Using inch (imperial) units of measurement.

Nominal Torque = Horse Power x 63025 / RPM = Application Torque (in-lbs)

While system nominal/application torque is important to know and understand, it is imperative that this NOT be the torque used to select the coupling.

Rather, the application torque must be multiplied by a service factor (application-specific) to ensure the coupling is robust enough to handle the unique challenges of that specific system.

Design Torque = Application Torque x Service Factor = Coupling Sizing Torque (in-lbs) Application service factors are generally available and listed in each manufacturer’s PDF product catalog… and it is this service factor that should be used when selecting your coupling.

Different manufacturers do rate their couplings differently (i.e. – some companies like publishing/marketing high catalog performance values… and will compensate for their higher catalog values by insisting on higher service factors), so you must use the manufacturer’s published rating and not a rating found elsewhere.

That said if you want to learn more, and become an expert on coupling service factors… there is an AGMA information sheet readily available to download and review.

Also read:

What is coupling?
Couplings and It’s Applications in Industry

How to Quickly Calculate Coupling Sizing Torque

Given how frequently coupling users (and application engineers) are required to calculate coupling sizing torque, various companies built apps that possess a free coupling sizing torque calculator that is readily available both on the internet, as well as in iPhone/Android smartphone form (pictured left).

In both cases, the user enters the horsepower, RPM, and service factor, and the required coupling sizing torque is automatically calculated. Values can also be calculated or converted between metric and inch (imperial) units by a toggle button at the top of the screen.


Thus coupling sizing is important as the proper measurement help the coupling to last long and works with heavier loads without being adversely affected. Thus it is highly important to properly measure or calculate the coupling sizing, whether manually or with the help of an advanced calculator or an app.

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