🔗 Bike Chain Length Calculator
Enter your chainstay length and your largest chainring and cog to get the correct chain length in inches and the number of links to run — using the standard chainstay formula.
Size to the big–big combination; on full-suspension bikes, confirm with the derailleur-wrap method.
🧮 Size Your Chain
🔗 Chain length
Cut your chain to the right length
Too long and the chain slaps, drops and shifts poorly; too short and you risk wrecking the derailleur — or the frame — the moment you shift into the big–big gear. A quick calculation before you break out the chain tool saves a lot of grief and wasted links.
This calculator applies the standard chainstay formula to turn your measurements into a length in inches and a whole, even number of links. Read exactly how the math works in the FAQ below.
❓ Frequently Asked Questions
What formula does this chain length calculator use?
It uses the standard rigid-drivetrain (Park Tool) equation, with all lengths in inches: chain length = 2 × chainstay length + (largest chainring teeth ÷ 4) + (largest rear cog teeth ÷ 4) + 1. The result is rounded to the nearest whole inch and multiplied by 2 to give the number of links, because a usable chain must have an even number of links (two links — one inner, one outer — per inch).
Where do I measure the chainstay length?
The chainstay length is the straight-line distance from the centre of the rear axle (dropout) to the centre of the bottom bracket. Measure it in inches; on most road and mountain bikes it's roughly 16 to 17.5 inches. This single measurement, together with your largest chainring and largest cog, is all the formula needs.
Why size to the largest chainring and largest cog?
The chain has to be long enough to reach the biggest-big-big combination — largest front chainring to largest rear cog — even if you'd never actually ride there, because that's the most chain the drivetrain can demand. Size it for big–big and every other gear will have enough chain. You can always remove links to remove slack, but you can't add chain that isn't there.
Does this work for modern 1x and clutch derailleurs?
The formula is a reliable starting point for traditional and many modern setups, but suspension bikes and some clutch or long-cage derailleurs need the chain wrapped through the derailleur to verify — the rear triangle also lengthens as the suspension compresses. For a full-suspension mountain bike, use this as a first estimate, then confirm with the derailleur-wrap method (big–big plus one or two links) before you cut the chain.