How to Measure a Bearing

Measuring a Bearing correctly is essential to ensure you order the right replacement. In most cases, you only need three key dimensions:

• Inside Diameter (ID) – the Diameter of the hole through the centre of the Bearing.

• Outside Diameter (OD) – the Diameter of the Bearing measured across the outside.

• Width (W) – the thickness of the Bearing.

These measurements are usually recorded in millimetres (mm). Some bearings are measured in inches (Imperial), particularly older or Imperial-standard Bearings.

Before you measure

Before measuring, check whether the Bearing still has a part number engraved on the side, such as:

• 6205-2RS

• 6004-ZZ

• 6308 C3

If the number is still visible, you may not need to measure the Bearing at all. Enter the part number on our website to see compatible replacements.

If the number is missing or unreadable, follow the steps below.

Step 1:  Measure the Inside Diameter (ID)

The Inside Diameter (ID) is the Diameter of the hole through the centre of the Bearing.

Measure from one inside edge directly across to the opposite inside edge using a Digital or Vernier Calliper.

Example: 25mm

Step 2: Measure the Outside Diameter (OD)

The Outside Diameter (OD) is measured across the widest part of the Bearing.

Ensure the Calliper is square to the Bearing for an accurate reading.

Example: 52mm

Step 3: Measure the Width (W)

Measure the thickness of the Bearing from one face to the other.

Example: 15mm

Example Bearing Size

If your measurements are:

• Inside Diameter (ID): 25mm

• Outside Diameter (OD): 52mm

• Width (W): 15mm

The Bearing size is written as:

25 × 52 × 15mm

This is the standard way bearing dimensions are listed.

Measure Using Digital Callipers

For the most accurate results, we recommend using:

• Digital Calipers

• Vernier Calipers

• Micrometres (for high-precision measurements)

Avoid using rulers or tape measures, as even a small error can result in ordering the wrong Bearing.

Metric or Imperial?

Most modern Bearings are manufactured to Metric dimensions, but some older machinery uses Imperial (inch) sizes.

If your measurements don't closely match a standard Metric Bearing, you may require an Imperial Bearing.

Our team can help identify the correct size if you're unsure.

Common Bearing Sizes

Some of the most common bearing sizes include:

What if the Bearing is Damaged?

If the Bearing is worn, seized or badly damaged:

• Clean it before measuring.

• Measure in several places to check for wear.

• If possible, measure the Shaft and Housing instead.

• Send us a photograph if you're unsure; we're happy to help identify it.

Measuring Different Types of Bearings

The same three measurements (ID, OD and Width) apply to most Bearing types, including:

• Deep Groove Ball Bearings

• Angular Contact Bearings

• Self-Aligning Ball Bearings

• Taper Roller Bearings

• Needle Roller Bearings

• Spherical Roller Bearings

• Thrust Bearings

Some specialist Bearings may also require additional measurements, such as Flange Diameter, overall height or Roller dimensions.

Measuring Tips

• Clean the Bearing before measuring.

• Measure in millimetres (mm) wherever possible.

• Use Digital Callipers for the best accuracy.

• Take measurements more than once to confirm the size.

• Check for an engraved part number before measuring.

Need Help Identifying Your Bearing? Our experienced team will identify the correct replacement, ensuring you get the right bearing for your application.

If you're unsure which size you need, see our Deep Groove Ball Bearing Size Chart here or provide the measurements, and we'll help identify the correct size.

Browse our range of Bearings here.