By Zencalcy Editorial TeamLast reviewed About us
Work out how many links your chain needs from your chainstay length, your chainring, and your largest cassette cog. The formula uses the half inch chain pitch and adds the wrap around the front and rear teeth. Chains come in whole pairs of links, so the result is rounded up to the nearest even number.
Work out how many links your bike chain needs.
links = 2 × (chainstay (mm) ÷ 12.7) + chainring teeth ÷ 2 + cog teeth ÷ 2 + 1, then round up to an even number
The 12.7 mm figure is the half inch chain pitch. The formula is a close estimate for a derailleur drivetrain; check the chain on the bike before shortening, since rear derailleur capacity and frame details can shift the right length.
| Symbol | Meaning |
|---|---|
| chainstay | Distance from the crank centre to the rear axle centre, in millimetres. |
| chainring | Teeth on the largest front chainring, or the only one on a single ring setup. |
| cog | Teeth on the largest rear cassette cog. |
With a 410 mm chainstay, a 50 tooth chainring, and a 32 tooth cog the raw figure is 2 × 32.28 + 25 + 16 + 1 = 106.57 links, which rounds up to 108 links.
Chain length is set so the chain can reach the largest front chainring and the largest rear sprocket without overstretching the derailleur. A standard estimate gives length in inches as twice the chainstay length, plus one quarter of the front teeth, plus one quarter of the rear teeth, plus one. The chainstay is the straight distance from the bottom bracket centre to the rear axle.
A worked example with a sixteen and a half inch chainstay, a 52 tooth chainring, and a 30 tooth sprocket gives 33 plus 13 plus 7.5 plus one, which is 54.5 inches. Since bicycle chain pitch is half an inch, that is about 109 links, which is rounded up to the next even number.
Chains are sold in even link counts, so round up to the nearest even number and join them with a quick link. The formula assumes the largest ring and the largest cog define the longest path the chain must cover, since a chain that is too short there would tear the derailleur apart.
The real test is on the bike. In the big ring and biggest cog the derailleur cage should still have slack, and in the small ring and smallest cog there should be enough chain that the cage is not pulled tight against itself. The arithmetic gets you close, then the derailleur tells you whether a link must be added or removed.
Continue with the Cycling Cadence Calculator, Cycling Power Calculator, or the Cycling Power Zones Calculator — or browse more cycling tools and all sports calculators.
Chains use inner and outer plates in pairs, so a chain always has an even number of links. An odd count cannot be joined without a special half link.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026