Bike Chain Length Calculator
Use this bike chain length calculator to find out how many links your chain needs: enter the teeth of the largest chainring and cog and the chainstay length, then read the link count.
Example: Drivetrain: Derailleur gears · Largest chainring (teeth) 50 teeth · Largest cog (teeth) 28 teeth · Chainstay length 410 mm → Chain length: 106 links (134.6 cm). Source: Sheldon Brown – Derailer Adjustment: Chain Length (big/big without derailleur, one full link of overlap). Updated: .
How it is calculated
A 50-tooth chainring, a 28-tooth cog and a 410 mm chainstay need about 106 links. The calculator works out the chain length that fits around ring and cog and adds the usual allowance for derailleur bikes.
How it is calculated
A roller chain has a pitch of 12.7 mm (half an inch). The length follows from the straight run between the wheels plus the links that wrap around ring and cog. The result is rounded up to an even number because a chain is made of pairs of inner and outer links. For derailleur bikes the proven rule applies: route the chain over the large ring and the largest cog, bypassing the derailleur, and let one full link (2 links) overlap.
Tips for checking
- A chain that is too short can damage the derailleur in the biggest gear. When in doubt, leave one pair more.
- On multi-ring cranks the largest ring counts, even if you rarely ride it.
- Wear stretches a chain: measure the elongation before you fit a new one.
Related: the bike gear ratio calculator, the speed calculator and the length converter.
Frequently asked questions
How long should a bike chain be?
For derailleur bikes: laid over the large ring and largest cog, plus one full link. The calculator uses tooth counts and chainstay length and returns the link count.
Why an even number of links?
A chain alternates inner and outer links. An odd count would need a half link, which is weaker.
How do I find the chainstay length?
Measure from the center of the bottom bracket to the center of the rear axle. With adjustable dropouts use the middle position; road bikes are usually around 405 to 415 mm.
What is the pitch of a chain?
The distance between two pins: 12.7 mm on bicycle chains, which is half an inch.
Sources and legal basis
- Sheldon Brown – Derailer Adjustment: Chain Length (big/big without derailleur, one full link of overlap)
- Wikipedia – Roller chain (pitch 1/2 inch = 12.7 mm, inner and outer links)
As of: · Editorial policy
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