Replace your chain when it has elongated 0.5% on an 11- or 12-speed drivetrain and 0.75% on 10-speed or fewer (Park Tool, which makes the wear gauges most shops use, also gives 1% for single-speed bikes). That elongation is tiny: over a 24-link section, a new chain measures 304.8 mm (12 in) and one at 0.5% measures 306.3 mm. But that millimeter and a half is the line between replacing just the chain and replacing the cassette and chainrings too. Below you’ll find how to measure it with a checker or a ruler, how often to do it, and what to do when you install the new chain.
What chain wear is
A bike chain has a pitch (distance between pins) of half an inch: 12.7 mm. With use, the pins and the holes in the inner plates wear away, and each link gains a few hundredths of a millimeter. The plates don’t stretch, but the chain as a whole gets longer, which is why people call it “stretch.”
The problem isn’t the chain itself, but what it does to everything else. A longer pitch stops seating at the bottom of the teeth and starts riding higher, near the tips. The teeth on the cogs and chainrings wear down to match that long chain. While the chain is below the limit, that extra wear is minimal. Past the limit, it speeds up, and when you finally put on a new chain it no longer meshes with teeth that have adapted to another one.
A worn chain gives no warning until it’s too late: shifting can feel fine until the chain is well past the limit. That’s why you measure instead of waiting to feel it.
When symptoms do show up, they’re these: the chain slips or skips under load on the cogs you use most and, in some cases, gets dragged up by the small chainring when you shift under load (chain suck). Before blaming the chain, make sure the derailleur is adjusted properly and the chain is clean.
Chain wear limits by number of speeds
The more speeds, the narrower the chain and teeth, and the less wear they tolerate (the chain width by speed chart gives the dimensions and which chains are compatible). This is Park Tool’s general reference, which its CC-4.2 checker (for 5 to 13 speeds) also uses:
| Drivetrain | Replace at | Length over 24 links | Difference from new |
|---|---|---|---|
| Single speed | 1% | 307.8 mm | +3.0 mm |
| 5 to 10 speed | 0.75% | 307.1 mm | +2.3 mm |
| 11 to 13 speed | 0.5% | 306.3 mm | +1.5 mm |
The lengths come from multiplying 24 links by 12.7 mm (304.8 mm, or 12 in) and adding the percentage. Each groupset maker can give its own limit, so if your drivetrain manual says otherwise, the manual wins.
How to measure chain wear
With a chain checker
It’s the fastest way: drop it into the chain and in two seconds you know if you’ve hit the limit. There are two common types:
- Two-ended gauges, like the Park Tool CC-3.2: one end reads 0.5 and the other 0.75. If the 0.5 side drops fully between the rollers, the chain has reached 0.5%. Flip the tool to check 0.75.
- Three-point gauges, like the Park Tool CC-4.2 or the Shimano TL-CN42: they touch the chain at three points over a longer section and read 0.5, 0.75 and 1%.
Not all of them measure the same. Zero Friction Cycling, an Australian lab that tests chains and lubes, compared more than a dozen checkers on a chain worn to exactly 0.5%: some read 0.3% (they’d have you keep riding a chain that’s already past it) and others 0.75% (they’d have you toss half-used chains). Among those that read correctly were the Park Tool CC-4 and the Shimano TL-CN42.
Steps for an accurate reading:
- Shift to the big chainring and a big cog, so the derailleur tensions the lower run of chain.
- Drop the checker in without forcing it: the end that “drops” has to fall in on its own, not be pushed.
- Measure in at least three different sections of the chain (five is better). It doesn’t wear evenly, and the most worn section is the one that counts.
- If you use wax, measure before rewaxing: fresh wax fills the gaps and gives a lower reading than the real one.
With a ruler
If you don’t have a checker, a steel ruler marked in inches works as an approximation:
- With the chain under tension, line up the edge of a pin with the zero mark.
- Count 24 more pins (12 full links). On a new chain, the last one lands right at 12 inches (304.8 mm).
- If it lands at 12 1/16 in (306.4 mm), the chain is at about 0.5%: if it’s 11- or 12-speed, replace it. At 1/8 in over (308.0 mm), it’s at about 1%: you’re late with any drivetrain.
A ruler has one drawback: 1/16 of an inch is just over a millimeter and a half, and judging it by eye is hard. Zero Friction Cycling recommends that if you measure length with a ruler or calipers, you replace the chain a bit early, around 0.3-0.4%.
The chain lift test
With the big chainring and the smallest cog, pull the chain away from the front of the chainring. If it lifts far enough that you can see several teeth, it’s worn or nearly so. It’s a hint, not a measurement: it tells you whether to get the checker out, not whether to replace the chain.
How often to check and how long a chain lasts
There’s no mileage that holds for everyone. The same chain can last twice as long or half as long depending on lube, how often you clean it, whether you ride in rain or dust, and how much power you put through it. Zero Friction Cycling stresses that wear doesn’t progress at a steady rate: it’s slow at first and speeds up once the lube is loaded with abrasive grit. You can measure at 3 months, find it perfect, and find it past the limit 3 months later.
Our practical routine:
- Check every 300 miles (500 km) or every month, whichever comes first. With a checker it takes half a minute.
- Check before a long ride or an event. A worn chain skips exactly when you push hardest, like when you stand up on a climb.
- Check more often if you ride in mud, dust or rain: dirt is what speeds up wear the most. How to keep it clean is explained in cleaning and lubing your chain.
- If the chain is very dirty, clean it before measuring: grime between the rollers also throws off the reading.
For an overview of everything worth checking and when, see the bike maintenance schedule by mileage.
Why replacing it on time saves money
The chain is the cheap part of the drivetrain. A cassette costs a lot more, and high-end chainrings even more. Park Tool sums it up: riding a chain past its limit wears out the cogs and chainrings sooner, and replacing a cassette costs far more than replacing a chain.
Zero Friction Cycling’s math is clear: if you replace the chain at 0.5%, a cassette usually lasts 2 or 3 chains and a set of chainrings 4 to 6. If you let the chain reach 0.6%, it starts wearing the teeth to fit itself; at 0.8% wear takes off, and a new chain no longer fits.
| If you replace the chain… | What usually happens |
|---|---|
| When it hits the limit | The new chain meshes fine; cassette and chainrings carry on |
| A bit past it (0.6-0.8%) | The new chain may skip on the most-used cogs |
| Way past it (1% or more on 11-12 speed) | You need a new chain and cassette, and sometimes chainrings |
If you install a new chain and it skips on the cogs you use most (but not on the ones you barely touch), the cassette had already adapted to the old chain. No derailleur adjustment will fix it: it’s time to change the cassette. If it also skips on rarely used cogs, first check how to adjust the rear derailleur.
Replacing the chain: length and quick link
How many links
A new chain comes longer than you need (usually 114 to 126 links) and has to be cut. The easiest way is to count the links on the old one, if it was the right length and you haven’t changed chainrings or cassette. If not, work it out with the chain length calculator, which uses the classic shop formula and each manufacturer’s method. Three examples from our calculations:
| Bike | Chainstays | Chainring × largest cog | Links |
|---|---|---|---|
| Road 2x | 410 mm | 50 × 34 | 110 |
| Road 2x | 405 mm | 52 × 30 | 108 |
| Mountain 1x hardtail | 435 mm | 32 × 52 | 116 (manufacturer’s method) |
More chainstay, chainring and cog combinations in the chain link chart.
The chainstays are the tubes that run from the bottom bracket to the rear axle; their length is in your frame’s geometry chart. If you’ve changed cassette or chainring, always recalculate: a bigger cog usually needs more links. We also explain it in 1x vs. 2x, because the difference between systems changes the math. If you save your bike in My Bike, the calculator picks up your chainrings, cogs and chainstays.
The quick link
Almost every 10-, 11- and 12-speed chain closes with a quick link (also called a master link): two half-plates that snap together without a special riveting tool. Not all of them are the same:
- According to Zero Friction Cycling’s roundup, SRAM Eagle, SRAM road AXS and Shimano 12-speed links are officially single-use: if you open the chain to clean it, the manufacturer wants a new one.
- Others, like YBN QRS 10-, 11- and 12-speed links, are sold as reusable up to 5 times.
- Always use a link for the same number of speeds and the same system as your chain. The SRAM road AXS chain is a different standard and doesn’t take chains or links from other systems.
Common mistakes
- Waiting for the chain to skip. By the time it skips, the cassette is usually already damaged. Measure regularly.
- Measuring just one section. The most worn section is what counts; measure in at least three places.
- Trusting any checker. Some read low and let you keep riding a worn-out chain; others read high.
- Using the 10-speed limit on a 12-speed chain. With 11 or 12 speeds the limit is 0.5%, not 0.75%.
- Not recalculating length after changing cassettes. A short chain can rip off the derailleur in the big-big combination; a long one can go slack in small-small. Check it with the gear ratio calculator and the chain length calculator.
- Reusing a single-use quick link. It’s a small part that takes all the force from your legs: if the maker says one use, it’s one use.
Frequently asked questions
How many miles does a bike chain last?
There's no fixed number: it depends on lube, cleaning, mud and power. The reliable approach is to check wear every 300 miles (500 km) and replace the chain when it reaches 0.5% (11-12 speed) or 0.75% (up to 10 speed).
If I replace my chain, do I need a new cassette too?
Not if you replace the chain in time. With chain swaps at 0.5%, a cassette usually lasts 2 or 3 chains and chainrings 4 to 6. If a new chain skips on the cogs you use most, the cassette was already worn.
How can I tell if my chain is worn without a tool?
With a ruler: line up a pin with zero and count 24 more pins. On a new chain the last one lands at 12 inches (304.8 mm); if it's 1/16 in (1.6 mm) past that, it's at about 0.5% and it's time to replace it.
Can you reuse a quick link?
It depends on the manufacturer. SRAM Eagle, SRAM road AXS and Shimano 12-speed links are officially single-use; others, like YBN QRS links, are rated reusable up to 5 times. Check what your chain's maker says.
Do bike chains really stretch?
The plates don't stretch: the pins and the holes in the inner plates wear, and each link ends up a little longer. That's why people call it "stretch" even though it's wear.
