Chain wear
Chain wear
Precise measurement and a mileage-based ballpark
12 links (tip-to-tip) is the standard. 10 links (roller-to-roller) is more accurate — smaller measurement error.
Replace at 0.5% elongation on 11- and 12-speed drivetrains, and 0.75% on 8-to-10-speed. A worn chain wears the cassette and chainrings too, so a cheap chain swapped in time saves an expensive drivetrain later.
Use a ruler on a chain under light tension. On a new chain, 12 full links span exactly 12 inches (304.8 mm) pin to pin. Around 12 and 1/16 inch means roughly 0.5% wear; 12 and 1/8 inch is about 1% and overdue. A dedicated chain-checker tool is quicker, but the ruler method is just as accurate.
As a chain stretches, its rollers no longer sit cleanly in the cassette and chainring teeth. Riding it past the limit grinds those teeth into a matching worn shape, so a fresh chain then skips — forcing you to replace the whole drivetrain instead of just the chain.
Yes. Narrower 11- and 12-speed chains have thinner sideplates and less material to give, so they hit their wear limit sooner — replace around 0.5%. Wider 8-to-10-speed chains tolerate up to about 0.75%. This calculator uses the right threshold for the drivetrain you pick.