Bearing Size Finder: How to Find the Right Bearing Every Time

Ordering the wrong bearing is one of the most common — and most avoidable — mistakes hobbyists and technicians make. A good bearing size finder process comes down to three measurements, and once you know how to take them correctly, matching a replacement bearing takes minutes instead of guesswork.

The Three Measurements Every Bearing Finder Needs

Every ball bearing is identified by three core dimensions, almost always written in the same order:

1. Bore (inner diameter) — the hole where the shaft passes through
2. Outer diameter (OD) — the outside width of the bearing
3. Width (thickness) — how thick the bearing is from face to face

A bearing labeled 5x11x4, for example, has a 5mm bore, 11mm outer diameter, and 4mm width. Once you have those three numbers, you can search by exact dimensions instead of relying on part numbers that vary between manufacturers.

How to Measure a Bearing for a Bearing Dimension Lookup

If the old bearing doesn’t have a legible size printed on the shield, measure it directly:

• Use a caliper (digital or dial) for accuracy — a ruler isn’t precise enough for most bearing sizes
• Measure bore, OD, and width separately, in millimeters
• Round to the nearest common size — most bearings are manufactured in standard increments, so a measurement of “10.9mm” almost always means the actual size is 11mm

Using Part Numbers as a Bearing Cross Reference by Size

Many manufacturers use standardized numbering systems (like the MR and R series for small bearings, or the 6000 series for larger ones) where the number itself encodes the dimensions. This is useful for a bearing cross reference by size, but part numbers can vary slightly between brands, so cross-checking actual measured dimensions is always the more reliable method.

Common Small Bearing Sizes We Stock

For hobbyist and precision applications, some of the most frequently ordered small bearing sizes include 3x8x4, 4x7x2, 5x9x3, 3x7x3, and 5x11x4 — covering everything from fidget spinners to RC motors to fishing reels. If you have exact measurements but aren’t sure which standard size they round to, send them to us directly.

When a Bearing Checker Tool Isn’t Enough

Online bearing checker tools can help narrow down options, but they can’t account for load requirements, seal type (2RS vs ZZ), or material needs (steel, stainless, ceramic) — all of which matter as much as raw dimensions for choosing the right bearing for your application.

Final Thoughts

Finding the right bearing size doesn’t have to be guesswork — three accurate measurements are usually all it takes. If you’ve got a bearing in hand and aren’t sure what it is, send us the measurements (or the old part) and we’ll confirm the exact match.

Shop Bearings By Size → [https://rcbearings.com/ball-bearings/]

---

Not sure what size you need? Call (978) 254-3987 — we’ll help you match it.