Every motorcycle chain has its size stamped right into the metal — no lookup required, if you know where to look and what the numbers mean. Here's exactly how to read it.
Where to find the stamp
Look at the outer side plate of the chain's links, along the exposed lower run between the sprockets. The stamp is usually small and shallow, and on a chain that's seen any real miles it's often buried under a layer of old lube and grit. You may need to rotate the wheel by hand and check a few links before you find one that's clean enough to read, or wipe one link down first. A chain that's genuinely caked can hide the stamp entirely — see How to Clean a Motorcycle Chain if a full clean is overdue anyway.
Decoding the number
The stamp follows a standard format, and it's simpler than it looks. The first digit (or first two, on larger sizes) tells you the pitch — the pin-to-pin spacing — in eighths of an inch. A 4 means 4/8" pitch, a 5 means 5/8" pitch, which is why 420 and 428 share a pitch family and 520, 525 and 530 share another. The remaining digits code the internal width between the plates: a higher number means a wider, heavier, generally stronger chain within the same pitch family. That's the full breakdown of what 520 vs 525 vs 530 actually means in practice, covered in this guide.
The letters that follow
After the number, a letter or two usually describes the chain's build rather than its size. An "H" typically marks a heavy-duty version of that size. An "X" or "XW" points to an X-ring chain — the ring profile that seals grease inside the pins under load. An "O" points to a standard O-ring design. These letters don't change what sprockets the chain fits; they describe durability and sealing, not pitch or width. If you're not sure whether your chain is O-ring, X-ring or standard, and why that distinction matters for maintenance, we cover it directly in O-Ring vs X-Ring vs Standard Chains, Explained Simply.
If the stamp is worn smooth or missing
On an old or heavily corroded chain, the stamp can wear away entirely. If that's the case, fall back to the owner's manual spec or a dealer parts lookup by model and year — see What Chain Size Does My Bike Use? for the full rundown of backup methods.
Quick answers
My chain's stamp is caked in grime — how do I read it?
Wipe down or spot-clean just the one link you're checking. A quick degrease of a single side plate is usually enough to expose the stamp without doing a full chain cleaning first.
What does the letter after the number mean, like 520H or 525X?
It describes the chain's build, not its size. H generally marks a heavy-duty version; X or XW points to an X-ring seal design; O points to a standard O-ring. Sizing and sprocket fitment come entirely from the number.
Do link-count numbers matter for sizing?
No — link count (the total number of links in the loop) determines chain length for your specific bike, not pitch or width. Two chains can share the exact same size stamp and still need a different link count depending on swingarm length and gearing.