Bearing guide
How to measure a bearing
Every bearing is identified by three sizes: the inside diameter, the outside diameter and the width. Measure those accurately and you can find an exact replacement in minutes.
Check for a part number first
Most bearings have a number stamped or printed on the side, on the seal or on the outer ring, such as 6205-2RS. If you can read it, you don't need to measure anything. Search by part number and you'll find the exact match. If the number is worn off or unreadable, carry on below.
Before you start
What you need
Bearing sizes are exact to the millimetre, so the tool matters. Clean the bearing first, because dirt and grease add to every reading.
Digital calipers
Read to 0.01 mm and switch between mm and inches. Cheap, quick and the easiest way to get it right first time.
Vernier calipers
Just as accurate as digital, but take a little practice to read. Fine if you already have a pair.
Ruler or tape measure
Not accurate enough. A bearing that's 1 mm out won't fit, and a ruler can't tell 25 mm from 25.4 mm.
The 3 measurements
Bore, outside diameter and width
Always measure in millimetres. Bearing sizes are written in the order bore × outside diameter × width, for example 25 × 52 × 15.
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1. Inside diameter (bore)
Use the small inside jaws of the calipers. Open them inside the hole until they touch both sides, and move them slightly to find the widest reading.
Measure in two or three places around the hole and use the largest figure. If the bearing is stuck or broken, measure the shaft it sits on instead. The shaft diameter is the bore size.
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2. Outside diameter
Use the main outside jaws. Close them across the outer ring, keeping the calipers square to the bearing, and read across the widest point.
If the bearing is damaged, measure the bore of the housing it sits in. That's the outside diameter you need.
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3. Width
Lay the bearing flat and measure across the side faces of the outer ring. Don't include any snap ring or collar.
On tapered roller bearings the inner and outer parts separate and can be different widths. Measure them assembled for the overall width, and note both part widths too.
Size checker
Metric or imperial?
Most bearings are metric and measure in whole millimetres. Older machinery, and some American and British kit, uses inch sizes like 1/2" or 1". Type a reading and we'll show the nearest match of each.
Enter any one of your three measurements in mm.
Common sizes
Deep groove ball bearing sizes
These three series cover a large share of everyday bearings in motors, pumps, gearboxes and machinery. Sizes in mm: bore × outside diameter × width. Tap a part number to see it in stock.
6000 series extra light
| Part no. | Size (mm) |
|---|---|
| 6000 | 10 × 26 × 8 |
| 6001 | 12 × 28 × 8 |
| 6002 | 15 × 32 × 9 |
| 6003 | 17 × 35 × 10 |
| 6004 | 20 × 42 × 12 |
| 6005 | 25 × 47 × 12 |
| 6006 | 30 × 55 × 13 |
| 6007 | 35 × 62 × 14 |
| 6008 | 40 × 68 × 15 |
Reading the part number
For 04 and above, the last two digits × 5 give the bore in mm: 6205 has a 25 mm bore. The letters after the number describe seals and fit.
| Code | What it means |
|---|---|
| 2RS / 2RSH | Rubber seals on both sides. Sealed and greased for life, best for dirty or wet conditions. |
| RS | Rubber seal on one side only. |
| ZZ / 2Z | Metal shields on both sides. Lower friction than rubber seals, good for higher speeds in clean conditions. |
| Z | Metal shield on one side only. |
| No suffix | Open bearing with no seals or shields. Lubricated by the machine it sits in. |
| C3 | More internal clearance than standard. Used in electric motors and where the bearing runs hot. Replace a C3 with a C3. |
| N / NR | A groove in the outer ring for a snap ring. NR means the snap ring is fitted. |
Know your type
Which bearing type is it?
Two bearings can share the same three sizes but be different types, so check which one you have before ordering.
Deep groove ball
How to spot it: a single row of balls, doesn't come apart. The most common type by far.
Angular contact ball
How to spot it: looks like a ball bearing, but one side of the outer ring is lower than the other.
Self-aligning ball
How to spot it: two rows of balls, and the inner ring tilts and swivels inside the outer ring.
Tapered roller
How to spot it: cone-shaped rollers. Separates into an inner cone with rollers and a loose outer cup.
Cylindrical roller
How to spot it: straight, short rollers instead of balls. One ring often slides off.
Spherical roller
How to spot it: two rows of barrel-shaped rollers, and the inner ring can tilt. Usually heavy-duty.
Needle roller
How to spot it: very thin, long rollers. Thin outer ring compared to its size.
Thrust
How to spot it: flat washer-style rings with balls or rollers between them, for loads along the shaft.
Housed units and pillow blocks: measure the shaft diameter, then the distance between the centres of the two bolt holes, and the height from the base to the centre of the shaft.
Avoid these
Common measuring mistakes
- Measuring the seal, not the ring
Rubber seals sit slightly below the rings. Always measure across the steel rings.
- Measuring a dirty bearing
Grease and rust add fractions of a millimetre. Wipe it clean first.
- Mixing up inches and millimetres
25.4 mm is 1 inch, not 25 mm. Use the size checker if you're unsure.
- Ignoring the suffix
A 6205-2RS and a 6205-ZZ are the same size but sealed differently. Match the letters too.
Got your three sizes?
Enter them in the bearing finder and we'll show every match. Still not sure? Send us a photo and your measurements and we'll help you identify it.