Common Ball Bearing Sizes Explained: How To Read The Numbers And Pick The Right One

Pick up any ball bearing and look at the number stamped into the side. Most people treat it like a serial number. It's not. That string of digits tells you almost everything you need to know, starting with the single most important dimension - the bore. Learn the trick, and common ball bearing sizes stop being a mystery; they become a language you can read at a glance.
I've lost count of how many buyers I've watched measure the outside diameter with calipers and still order the wrong bearing, because they never checked the hole. So let's start there, because the bore is where common ball bearing sizes are really defined. On a standard metric deep groove ball bearing, the last two digits of the model tell you the bore - and it's embarrassingly simple: multiply them by five. A 6204? That's 04 × 5 = 20 mm bore. A 6305? 25 mm. The catch is the first few models, where 00, 01, 02, and 03 are special cases standing for 10, 12, 15, and 17 mm respectively. Remember those four numbers and you can decode most of the common ball bearing sizes on any shelf without touching a caliper. The reason this works is that common ball bearing sizes follow international standards, so any supplier's chart lines up with the next one's.
Once you have the bore, the rest is a family affair. Every series has its own character, and knowing which family you're in narrows the choice fast.
The 6200 series is the backbone of common ball bearing sizes for everyday mid-duty work. Bore runs roughly from 10 to 30 mm, with a compact but capable section - 6202 is 15×35×11, 6204 is 20×47×14, 6206 is 30×62×16. You'll find this family in electric motors, pumps, gearboxes, conveyor rollers, and a thousand industrial odds and ends. If a customer hands you a dusty old motor and asks for "the usual bearing," the 6200 series is what they usually mean, which is why it dominates so many lists of common ball bearing sizes.
Need more muscle? That's the 6300 series, the other heavyweight half of common ball bearing sizes. Same bore range, but a wider section and bigger balls, so it shrugs off higher radial loads - 6300 is 10×35×11, 6301 is 12×37×12, 6304 is 20×52×15. The trade-off is speed: the chunkier the bearing, the lower its limiting speed, so 6300s turn up where load matters more than RPM - machine tools, fans, agricultural equipment, that sort of thing.
On the slim side, the 6000 series is the thinnest of the common ball bearing sizes in this group, built for high speed rather than brute force. 6000 is 10×26×8, 6001 is 12×28×8, 6004 is 20×42×12. These are the ones you see in small motors, instruments, and wherever designers are fighting for every millimeter of space. And at the small end, the 6800 series and old favorites like the 608 round out the common ball bearing sizes you'll meet in miniature and hobby applications - skateboards, pulleys, small rollers - where light, fast, and quiet beats heavy and tough.
For a quick lookup, here are the common ball bearing sizes I keep going back to, in bore × outer × width millimeters:
6200 - 10 × 30 × 9
6201 - 12 × 32 × 10
6202 - 15 × 35 × 11
6203 - 17 × 40 × 12
6204 - 20 × 47 × 14
6205 - 25 × 52 × 15
6206 - 30 × 62 × 16
6300 - 10 × 35 × 11
6301 - 12 × 37 × 12
6302 - 15 × 42 × 13
6303 - 17 × 47 × 14
6304 - 20 × 52 × 15
6000 - 10 × 26 × 8
6001 - 12 × 28 × 8
6004 - 20 × 42 × 12
6800 - 10 × 19 × 5
608 - 8 × 22 × 7
But common ball bearing sizes are only half the story. The letters after the number matter just as much, because they tell you how the bearing is protected. ZZ means thin metal shields on both sides, good for keeping big debris out while the bearing still spins freely. 2RS means rubber contact seals, the best defense against dust and moisture, pre-greased and essentially maintenance-free. Open bearings, with no suffix, are for clean, light-duty spots where you lubricate yourself. Same numbers, different personality - that's the part a size chart can't show you, and it's why the common ball bearing sizes question never has just one answer.
The same logic applies to material, of course. As with all common ball bearing sizes, the steel decides the real-world limits: standard chrome steel for dry indoor duty, stainless for anything wet or corrosive, ceramic hybrids when speed and weight are critical. Choose the size for the fit, then choose the seal and material for the environment. Too many orders get the first right and the second wrong.
One honest piece of advice: when you need a bearing, don't guess from a photo. Read the number, confirm the bore, check the width, and verify the suffix against the part you're replacing. And if you're buying in quantity, treat sourcing the way you'd treat the spec - buy from a factory that keeps the full range and will tell you exactly what's inside. BLH Bearings in Dongguan carries the 6000, 6200, and 6300 series with full size charts on the site, plus stainless, sealed, and non-standard variations, with OEM and ODM support if you need something beyond the catalog.
That's the practical tour of common ball bearing sizes. The numbers aren't random; the families each have a job; and the suffix and material finish the sentence. Learn to read the stamping, and you'll never stand in front of a bin of bearings guessing again - you'll know exactly what you're holding before you pick it up.