Chain Length Calculator
Enter your chainstay length and your biggest chainring and cog to get the number of links to run — before you break a link too many.
Cut once, ride confidently
A chain that is too long slaps the stay and shifts lazily; one that is too short can destroy a derailleur the first time you drop into the big cog. The formula here has sized chains in shops for decades because it works from the two things that actually set the length — how far apart the axles sit and how big your biggest ring and cog are.
Changing your gearing? Run the numbers in the Gear Ratio Calculator first, then come back here to resize the chain for the new setup.
Frequently Asked Questions
How does the chain-length formula work?
It uses the long-standing rigid-drivetrain equation: twice the chainstay length in inches, plus a quarter of the largest chainring's teeth, plus a quarter of the largest cog's teeth, plus one. That gives the shortest chain in inches that will still shift onto the biggest ring–cog combination. A chain has a half-inch pitch, so there are two links per inch; the result is rounded up to the nearest even number of links, because a chain only joins and breaks at whole links.
Where do I measure the chainstay?
Chainstay length is the straight-line distance from the centre of the bottom-bracket axle to the centre of the rear axle (dropout). It is often listed in your frame's geometry chart, which is the easiest place to find it; otherwise measure it directly in millimetres and enter that. On a full-suspension bike the effective chainstay changes as the suspension moves, which is why you also check the chain at full compression.
Do I size to the big-big combination on a 1x drivetrain?
Yes. Even though you would rarely ride the very largest cog with a big chainring, sizing to that worst-case combination guarantees the chain is long enough to reach it without wrenching the derailleur. On a modern 1x setup that means your single chainring and your biggest cassette sprocket. The formula deliberately gives the shortest chain that still covers it.
Should I trust the number exactly on a full-suspension bike?
Use it as your starting length, then verify on the bike. Many full-suspension frames grow their effective chainstay as the shock compresses, so run the chain through the largest cog and cycle the suspension to full travel — the derailleur should still have tension and not yank tight. If it does bind, add a link or two. Always test-shift through the whole cassette before your first ride.
A starting length from the standard formula, not a final cut. Always verify chain tension at full suspension compression and test-shift the full range before riding.