Before you buy a replacement chain, a new brush, or anything else sized to your chain, you need one number — and most riders have never actually looked it up. Here's the fastest way to find it, in order of how little work each one takes.
Fastest: your owner's manual
The specifications section lists chain size directly, usually right next to final drive ratio and sprocket tooth counts. No guessing, no crawling under the bike. If you don't have a paper copy, most manufacturers post manuals or spec sheets on their support sites, searchable by model and year.
No manual handy? A quick search for "[your bike model] chain size" against the manufacturer's own spec page or a dealer parts lookup gets you the same answer. Skip forum threads for this one — riders misremember spec numbers constantly, and a wrong chain size is an expensive guess.
Just as fast: the chain itself
Every motorcycle chain has its size stamped directly into the metal, usually on the outer side plate of a link. If the chain on the bike right now is the correct stock size — which it usually is unless someone's converted it — that stamp is your answer, no lookup required. We cover exactly what those stamped numbers and letters mean in How to Read the Size Stamped on Your Motorcycle Chain.
One catch: a grimy, caked chain can hide that stamp completely. A quick clean of just the one link you're checking is usually enough to expose it.
Rough guide by bike type — verify, don't assume
Small-displacement bikes and off-road machines tend to run smaller chains; bigger street bikes run bigger ones. As a general pattern: pit bikes, mini motos and small ATVs commonly run 415, 420 or 428. Full-size street bikes, larger dirt bikes and quads commonly run 520 or 525. Bigger cruisers and some touring bikes step up to 530. We go deeper on the small end in Pit Bike and Mini Moto Chain Care and on quad-specific quirks in ATV and Quad Chain Maintenance, and the full breakdown of what the numbers themselves mean is in 520 vs 525 vs 530 Chains: Sizes and Conversions Explained.
Treat this as a starting expectation, not a final answer. Plenty of bikes get converted to a different size chain for weight or gearing reasons, and "what size does this class of bike usually run" is exactly the kind of assumption that gets someone the wrong part.
Why guessing costs you twice
A chain that's the wrong pitch won't sit on the sprocket teeth correctly — it either won't fit at all or wears itself and the sprockets out fast if it's forced on. A chain that's the wrong width can look close enough to tempt you and still be a mismatch. Confirm the number before you order anything, brush included — sizing determines which cleaning brush actually fits, not just which chain to buy.
Quick answers
Where's the fastest place to find my bike's chain size?
The owner's manual specifications section, or the stamp on the chain's own side plate if the chain is still stock. Both are faster and more reliable than guessing from the bike's class or engine size.
Can I tell chain size just by looking at the bike?
Not reliably. You can make an educated guess from bike type — small bikes tend toward smaller chains — but manufacturers and owners both deviate from that pattern often enough that it's not safe to order parts against a guess.
What if my bike's chain has been swapped from stock?
Then the stamp on the current chain tells you what's actually installed, which may not match the original factory spec. Check the stamp itself rather than looking up the bike's stock spec if you're not sure the drivetrain is original.