How to measure a bearing?




What is a bearing ?

A bearing is a mechanical component used to facilitate rotation between two parts. It reduces friction between moving parts, which helps improve the efficiency and life of machinery and equipment.

Bearings typically consist of an inner ring, an outer ring and rolling elements such as balls, rollers or needles that are housed between the two rings. Ball bearings are the most commonly used. Regardless of the type of bearing, they are manufactured in a variety of sizes to suit different applications.

Why measure a bearing?

Generally, the bearing reference is written directly on the bearing. The part number can be engraved on the rings, on the seal or on the sealing flange. If your bearing does not have a part number, the only way to identify it is to measure it.

The measurement of a bearing can be done with a caliper, which is the most accurate tool to do so. This tool allows you to measure the inside diameter, the outside diameter and the thickness of the bearing. 

What are the different steps to measure a bearing?

  1. Get a caliper. This is the tool you must have to take accurate measurements of the bearings. You can choose an analog caliper or a digital caliper, which shows you the measured value directly.
  2. Measure the inside diameter of the bearing. To do this, you must position the inner tips of the caliper on the walls of the inner ring. You can then take the corresponding measurement. To do this, you have two possibilities: the measurement is a whole number or the measurement is a decimal number.

If it is a whole number, the 0 on the moving part will fall right on one of the lines on the fixed part. For example, 20 mm as below.

If it is a decimal number, take the line closest (to the left) to the 0 which will give you the integer part of your measurement. For the decimal part, take the graduation of the mobile part which will be perfectly aligned with one of the lines of the fixed part. For example, 20.5 mm as below.


3. Measure the outside diameter of the bearing. Position the outer tips on the ends of the outside diameter and take the measurement as before.

4. Measure the thickness of the bearing. Position the bearing in profile, facing you, and place the outer lugs on each side of the bearing and read the corresponding measurement.