How to measure a bearing
How to measure the bore, outer diameter and width of a bearing with a caliper, common mistakes, and finding a bearing from its size.
Last updated: 6 November 2026
If the code on a bearing has worn off or is unreadable, you can find it from its size. Standard bearing sizes are fixed, so three measurements narrow the options down a lot.
What you need
A metric caliper is enough. Measurements taken with a ruler are often misleading.
The three measurements
| Measurement | Where to take it | Symbol |
|---|---|---|
| Bore | Inside the inner ring | d |
| Outer diameter | Across the widest part of the outer ring | D |
| Width | From one side face of the ring to the other | B |
Write the result as bore × outer diameter × width, for example 25 × 52 × 15.
Measuring accurately
- Clean the bearing; dirt and rust add to the reading.
- Hold the caliper square to the bearing and measure in two or three places.
- Note decimals without rounding. Values such as 25.4 or 19.05 may point to an inch bearing (1 inch = 25.4 mm).
- On tapered roller bearings the inner and outer rings have different widths; measure the total width with both rings together.
Size alone may not be enough
Different types share the same size. For example, 25 × 52 × 15 can be a deep groove ball bearing (6205), an angular contact ball bearing (7205), a self-aligning ball bearing (1205) or a cylindrical roller bearing (NU 205). So also check:
- Does it have balls or rollers?
- Are the sides open or closed? (2RS vs ZZ)
- Do the rings separate from each other?
Searching by size
Enter the three measurements in the Bearing finder or choose from the size list. For example, the 25 × 52 × 15 page shows the options in this size and their stock. If you are not sure, send us a photo of the part.