How Bearings are Measured

There are actually several ways you can do this, and some are far easier than others. The measurement of a bearing consists of:

  • Inside diameter
  • Outside diameter
  • Thickness

The easiest way to measure a bearing is simply to examine its reference number and look up that number on the manufacturer’s website. However, the reference number often rubs off over time, so it’s not always possible to check.

However, if you are interested in how a ball bearing is measured, continue reading. If you are measuring it on your own, simply use a caliper to measure all necessary dimensions.

If you are measuring a ball bearing for example, the measurement would typically be stated something like 5x11x4. Measurements for bearings are often, but not always, stated in metric terms.

In the case of a 5x11x4 bearing, the inside diameter is 5 mm, and would fit the corresponding shaft. The outside diameter is 11 mm, while the bearing is 4 mm thick.

If you are doing this on your own, the best thing you can do is use the reference number. That way, you know precisely what the measurement of your bearing are.

Other tips on measuring ball bearings:

    • Whether or not your bearings have flanges does not affect the measurement of their diameter.
    • While the measurement difference between bearings may not seem large, it is important to get the bearing with the best fit. Bearings that are too large, of course, won’t fit. Bearings that are too small, however, make your machines run less smoothly, wear out faster, and have a greater chance of breaking down.
    • There are many different standards-making bodies for various bearing tolerance classes.

If you need specific information on a replacement bearing you can always call a bearing supplier such as Dalton Bearing Services at

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