Bearing Size Chart

Every metric ball bearing is described by three numbers: bore × outer diameter × width, all in millimetres. A 6205 is 25 × 52 × 15 mm. Once you can read those three figures out of a part number, you can size almost any bearing without a catalogue.

The Three Dimensions

• Bore (d) — the inner hole, which sits on the shaft. This is the dimension you almost always start from.
• Outer diameter (D) — the outside of the bearing, which sits in the housing.
• Width (B) — how thick the bearing is along the shaft.

Working Out the Bore From the Number

The last two digits of a standard bearing number give the bore. Four codes are exceptions, and everything above them follows a simple rule.

Bore code	Bore diameter	Rule
00	10 mm	Fixed exception
01	12 mm	Fixed exception
02	15 mm	Fixed exception
03	17 mm	Fixed exception
04 and above	Code × 5	04 = 20 mm, 08 = 40 mm, 20 = 100 mm

So a 6205 has bore code 05, giving 5 × 5 = 25 mm. A 6820 has bore code 20, giving 20 × 5 = 100 mm.

Same Bore, Different Bearing

The bore does not tell you the whole story. The second digit sets the dimension series — how much metal surrounds that bore. Here are five bearings from our database that all fit a 10 mm shaft:

Bearing	Bore	Outer diameter	Width	Character
6800	10 mm	19 mm	5 mm	Extra thin section
6900	10 mm	22 mm	6 mm	Thin section
6000	10 mm	26 mm	8 mm	Extra light
6200	10 mm	30 mm	9 mm	Light
6300	10 mm	35 mm	11 mm	Medium

All five fit the same shaft. The 6300 carries far more load than the 6800, but needs a housing bore almost twice as large and takes more than twice the width. That trade-off — load capacity against space — is the whole point of having series.

Choosing a Series

• 68 and 69 — thin section. Use where radial space is tight: robotics, bicycle hubs, instruments, compact gearboxes.
• 60 — extra light. A general-purpose choice where loads are modest.
• 62 — light. The most widely stocked series; usually the default if you have room.
• 63 — medium. Heavier loads, lower speeds, more robust.
• 64 — heavy. Highest load capacity for a given bore, and the bulkiest.

Measuring an Existing Bearing

If markings have worn off, record bore, outside diameter and width with calipers on clean, undamaged surfaces. Measure at several positions and record the range of readings; do not assume the largest reading is correct. Wear can enlarge the bore, reduce the outside diameter or affect the reading unevenly. Use dimensions to find candidates, then confirm the full designation and application requirements.

Worked Example: 20 mm Bore, Two Different Bearings

A bearing measuring approximately 20 × 47 × 14 mm points to the 6204 size. A 6304 also has a 20 mm bore, but measures 20 × 52 × 15 mm. The extra 5 mm outside diameter and 1 mm width mean it does not fit the same housing simply because the shaft size matches.

Record the original suffixes before removing the bearing: seals, clearance and tolerance are separate from the three boundary dimensions. If those markings are missing, consult the machine documentation rather than inferring them from size.

Browse the full range on our bearing series index, or read how to read bearing numbers for prefixes and suffixes.

Related: Best Brands for 6205 — Complete Comparison Guide — Compare SKF, NSK, NTN, Timken, FAG, and Koyo 6205s with prices and ratings.

Explore specific sizes: See our detailed guide for the popular 6304 (20mm bore, 52mm OD) or the 6205 (25mm bore, 52mm OD) with brand-by-brand recommendations.