Simple Guide to measuring a Ball Bearing.

Replacing a worn-out bearing, verifying specifications, or troubleshooting a machine, having the knowledge of how to measure a ball bearing correctly is essential. Ball Bearings might look small and simple, but accurate measurement prevents premature wear, ensures you get the right fit, and saves you from costly mistakes and downtime.

Here, in this post, we’ll break down the process of measuring a ball bearing step by step.

Dimensions of a Ball Bearing

Each bearing has three primary dimensions that you’ll want to measure:

• Inner Diameter (ID) – Hole size in the middle of the bearing (fits onto the shaft).
• Outer Diameter (OD) – Total width across the outside of the bearing.
• Width (W) – Thickness of the bearing.

These measurements together, will help you identify the correct bearing or confirm the size in a parts catalog.

Tools Required

• A Digital or Vernier Caliper – Gives accurate measurements (to the nearest 0.01 mm or 0.001 inch).
• Micrometer (optional) – Highly precise readings.
• Measuring Tape or Ruler – For quick checks but not for precision.

Step-by-Step Measurement Process

1. Measuring the Inner Diameter (ID)

• Open your caliper jaws and place them inside the central hole of the bearing.
• Expand the jaws until they make contact with the inner ring.
• Record the reading — this is the shaft size your bearing will fit on.

For example, an ID of 20 mm means the ball bearing will fit a 20 mm shaft.

2. Measuring the Outer Diameter (OD)

Place the caliper jaws around the outside edge of the bearing.

Make sure you measure across the widest point of the bearing.

Write down the result, this tells you the housing size required.