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Chain Length Calculator — Correct Chain Length
Calculate the correct chain length for your drivetrain setup.
How We Calculate This
Chain Length Formula
- Links = (2 × Chainstay / 12.7) + (Largest chainring + Largest sprocket) / 2 + 2
- This is Park Tool's simple equation L = 2C + F/4 + R/4 + 1 with C in inches. That form gives the length in INCHES, and one inch is two links, so it is doubled here to give the count printed on a chain box
- Round up to the nearest even number: a chain joins inner plate to outer plate, so its length is always even
- 12.7 mm = fixed bicycle chain pitch (½ inch, ISO 606); the +2 links give derailleur take-up at big-big
- 1x with a ≥42T cog (long-cage clutch derailleur): Park Tool's 42T+ rule is 4 rivets (two inches) total take-up, which replaces the standard 2 rivets — i.e. 2 extra links over standard for chain wrap
Frequently Asked Questions
A too-long chain may not tension properly, causing poor shifting, chain slap, and risk of the chain dropping off. The rear derailleur cannot take up the excess slack.
A too-short chain is dangerous. Shifting to big-big (largest chainring + largest sprocket) can rip off the rear derailleur. It also causes excessive drivetrain stress.
Most new chains come with 114, 116 or 118 links, and you remove links to suit your bike. A link is one 12.7 mm pitch, roller to roller, so a 116-link chain measures about 147 cm. That is the number printed on the box and the number this calculator gives you.
A half-link is a real and separate part: an offset link half a pitch long, used to fine-tune chain length on singlespeed and BMX bikes where there is no derailleur to take up slack. It is not another word for a link. Chain length is always quoted in whole links.
Route the chain through the big chainring and big sprocket, bypassing the derailleur. Pull tight, find the closest joinable rivets, then add 2 links (2 rivets, one inch). This is the most reliable method for most bikes.
Yes, significantly. Longer chainstays (touring, gravel bikes at 420-445 mm) need longer chains than short chainstays (road race bikes at 400-410 mm).
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Last updated: February 2026
All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.