Caleb MorganBy Caleb Morgan

Updated November 2026

A bike bearing size chart lists the inner diameter, outer diameter and width of the bearings used in hubs, headsets, pedals and bottom brackets. Once you can read one, you can match a replacement bearing to your bike without guesswork. This guide shows you how to measure the old bearing, confirm the code and check the fit before you buy.

Understand the Three Dimensions That Matter

Every standard bearing is described by three numbers, usually written in millimeters. The bore is the inner diameter, the part that sits on the axle or spindle. The outer diameter, or OD, is the outside edge that presses into the housing. The width is how thick the bearing is from one face to the other. Most bearing codes follow a pattern such as 6902 or 6001, where the last two digits often relate to the bore, so a 6902 typically has a 15 mm bore.

Shopping for one? See our guide: 5 Best Road Bike Shoe Size Charts (2026): Expert Picks.

Measure the Old Bearing or the Bearing Seat

If the old bearing is still in good shape, measuring it gives you the most reliable numbers. If it is damaged or missing, measure the housing it came from instead. Use calipers for accuracy, and take each measurement twice to rule out errors.

  1. Clean the bearing or seat so grease and grit do not throw off the reading.
  2. Measure the bore across the inner ring at its widest point.
  3. Measure the outer diameter across the outer ring.
  4. Measure the width between the two faces.
  5. Look for printed markings on the bearing face and compare them with a bearing size chart to confirm the code.

Match the Bearing Type to Its Position

Size alone is not enough. Hubs, headsets and bottom brackets use different bearing styles, and a bearing that fits the bore may still be wrong for the job. Headsets often use angular contact or cartridge bearings, while many bottom brackets use sealed cartridges with a specific spindle diameter. Check whether your bike uses loose ball bearings or sealed units, because mixing them can cause early wear or rough rotation.

Common Bearing Positions on a Bike

Location What to Measure Typical Note
Front or rear hub Bore, OD, width Often sealed cartridge bearings
Headset Bore, OD, stack height Check whether the cups are press-fit
Bottom bracket Spindle size, shell width Fit depends on the frame standard
Pedal Bore, OD, width Usually small sealed bearings

Check the Fit Before You Install

Before pressing anything in, confirm that the new bearing matches the old one in all three dimensions. A bearing that is even slightly oversized can crack the housing, and one that is undersized will spin or work loose. Dry-fit the bearing into the housing and check for smooth, even rotation. If it binds, stop and recheck your measurements rather than forcing it.

  • Digital calipers give quick, accurate readings of bore, OD and width. View on Amazon
  • A bearing press set helps seat bearings evenly without damaging the housing. View on Amazon

Common Mistakes

  • Measuring only the bore and assuming the rest will match.
  • Ignoring whether the bearing is sealed or open, which affects maintenance.
  • Hammering a bearing into place instead of using a press or proper driver.
  • Buying by bearing code alone without checking the bearing style for that position.
  • Skipping the dry-fit check before greasing and installing.

For more on sizing other bike parts, see Trek Bike Size Chart: How to Find Your Right Frame Size and Wheel Size Chart for Bike Computer: Set the Right Tire Circumference.

FAQ

Can I use a bearing with a different width?

Sometimes, but only if the housing has room and the spacers can be adjusted. A different width can change preload or alignment, so check the bike’s specifications first.

What if the bearing has no readable markings?

Measure the bore, OD and width, then compare those numbers with a size chart. Taking the old part to a bike shop can also help confirm the fit.

Do I need to replace bearings in pairs?

Usually you should replace both bearings in a hub or headset together so they wear evenly and rotate smoothly. Mixing old and new can cause uneven feel.

Conclusion

A bike bearing size chart is only useful when you measure accurately and match the bearing style to its position. Take three careful readings, confirm the code, and dry-fit before installing. If you are unsure about a repair involving headsets or bottom brackets, consult a professional bike mechanic.

Ready to choose one?

Caleb Morgan

About Caleb Morgan

Caleb Morgan is part of our editorial team and reviews and edits our cycling for beginners guides, checking product details against manufacturer specifications and owner feedback.