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Free workshop tool

Bike Chain Length
Calculator.

Enter your chainstay length and your largest chainring and cog to get the correct chain length in links and inches.

Your drivetrain
Chain length
108 links
Length 53.5 in
In centimetres 135.9 cm
Size on the largest chainring and largest cog with the chain out of the rear derailleur, then confirm the derailleur is not overstretched before you cut.

Results update as you type. This is the target length; always double check against your rear derailleur capacity before cutting a chain.

The maths

How the calculator works

It uses the standard chain sizing equation from your chainstay and your biggest gears.

=
The formula Length in inches = 2 x chainstay + largest chainring / 4 + largest cog / 4 + 1.
CS
Chainstay The distance from the rear axle to the bottom bracket. It sets the baseline wrap of the chain.
BB
Big-big gears Use the largest chainring and largest cog so the chain is long enough for every gear.
L
Even links Inches are doubled to links, then rounded up to an even number, because plates alternate inner and outer.
+
Derailleur check The plus 1 covers derailleur wrap. Always confirm the cage is not overstretched in big-big before cutting.

The equation gives a reliable target, but frames and derailleurs vary. Treat the result as your starting length, thread the chain through the drivetrain, and check tension in both the smallest and largest gears before you break it.

Want a printable home mechanic cheat sheet?
A one-page drivetrain and torque reference for your workshop wall is coming soon to our shop.
FAQ

Chain length FAQ

Measure your chainstay (rear axle to bottom bracket), then use the standard formula: chain length in inches equals 2 times the chainstay plus the largest chainring divided by 4 plus the largest cog divided by 4 plus 1. Round up to an even number of links. This tool does the maths for you.

A typical road or mountain chain runs between 104 and 116 links depending on frame size and gearing. New chains usually ship at 116 or 118 links so you can cut them to your exact length. Chains are always an even number of links because inner and outer plates alternate.

Length in inches equals 2 times chainstay length, plus largest chainring teeth divided by 4, plus largest cog teeth divided by 4, plus 1. Multiply the inches by 2 to get links, then round up to the nearest even number. It is the method Park Tool and most mechanics use.

Yes. Size using the largest chainring and the largest cog, without the chain through the rear derailleur, then add the standard allowance. This guarantees the chain is long enough for every gear and the derailleur is never overstretched in big-big.

It can. On many full suspension frames the effective chainstay grows as the suspension compresses, so measure with the rear shock at its longest chainstay position (often at sag or bottom out per the maker). When in doubt, add a link and confirm the derailleur is not overstretched.

Both cause problems. Too long and the chain sags, slaps and shifts poorly in small-small; too short and it can jam or damage the derailleur in big-big. The calculated length keeps tension correct across the full gear range.