How to Measure a Bearing

This quick guide will show you how to measure a bearing. Generally most bearing references are either laser stamped or engraved deep onto the bearing – having the bearing reference number is the quickest way to determine which bearing you require. However, due to overall wear and tear these could eventually rub off and make it harder to identify. To get the measurements you will need either a Vernier Calliper or even an everyday Ruler will make do.

Two verniers one smaller and one larger with a deep groove ball bearing in the center

Most of the bearings at Arrow are metric in size – but they can also be in Imperial. Keep in mind that most bearing sizes are inch sizes or full mm e.g. 19.05mm would be 3/4 inch. Each bearing has an Inside Diameter (d), Outside Diameter (D) and Width Diameter (B).

You can search and narrow down the results for a bearing using our search criteria boxes on the left hand side of a page – e.g. using the d or D as a reference. Once you have correctly identified a bearings size you may need to find out whether it comes complete with shield/s or seal/s – known as the suffix in the bearing reference.

Vernier measuring the inner diameter of deep groove ball bearing

Step 1

Insert the outer anvils of the caliper into the bore of the bearing as demonstrated. In the picture and open the Vernier caliper until there is a good fit with each other. This will give you the bore size of the bearing.

Vernier measuring the outside diameter of deep groove ball bearing

Step 2

Place the jaws of the calliper around the outside of the bearing until it's a good fit. This will give you the outer diameter size of a bearing.

Vernier measuring the width of the deep groove ball bearing

Step 3

As you have done previously, to measure the width of the bearing by placing the jaws of the calliper around the width as shown in the diagram. Be sure it's a good fit.

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