Chain Wear Checker
Replace a chain when it has worn 0.5% longer on 11-speed and up, 0.75% on 10-speed or fewer, and 1.0% on a single-speed (Park Tool). With a ruler: put a rivet on zero and count 24 rivets — a new chain is exactly 12 inches, and more than 1/16 inch over (about 0.52%) means it’s due. Replacing it in time saves the cassette and chainring.
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Your chain
Wear
Elongation
0.26%
Your limit
0.75%
5 to 10 speeds
Limit on a ruler
12.090in
307.1 mm
Plenty of life left
Replace the chain in time
$35 + chain
Wait until it skips: chain + cassette
$75 + parts
How this was calculated
“Chain stretch” is really wear: in Park Tool’s words, the rivets and rollers “begin to wear out, giving the illusion of stretching.” Keep the chain under light tension while you measure.
Worked example
A 9-speed e-bike chain measuring 12 1/16 inches over 24 rivets
Elongation: (12.0625 − 12) ÷ 12 × 100 = 0.52%. Limit: 9-speed falls under Park Tool’s “10-speed or fewer”, so 0.75%. Verdict: 0.52 ÷ 0.75 = 69% of the way there — plan a chain soon. On an 11-speed drivetrain the same reading is already at the 0.5% limit.
Reference
Chain wear limits
| Drivetrain | Replace at | Over 24 rivets (in) | Over 24 rivets (mm) |
|---|---|---|---|
| Single-speed / internal hub | 1% | 12.120 | 307.8 |
| 5 to 10 speeds | 0.75% | 12.090 | 307.1 |
| 11 speeds or more | 0.5% | 12.060 | 306.3 |
How to use it
In 4 steps
- 1Shift so the chain sits on a middle cog and keep it under light tension.
- 2With a ruler: line a rivet up at zero and count 24 more rivets along the chain. Read where the 24th sits — 12 inches is new.
- 3Or drop in a chain checker and note which side sinks all the way in.
- 4Pick how many speeds your bike has — that sets the limit.
Why an e-bike chain matters more
A chain doesn’t really stretch. Its rivets and rollers wear, and the spacing between links grows — which Park Tool calls “the illusion of stretching.” A worn chain no longer matches the teeth, so it wears the cassette and chainring to its own shape. Replace it in time and it’s a chain; wait until it skips and a new chain won’t sit on the worn cogs, so it’s a chain and a cassette.
E-bikes are hard on chains: heavier bikes, motor torque going through the drivetrain on mid-drives, and more miles. That makes the check worth doing every few hundred miles rather than once a year. Narrow 11- and 12-speed chains have less wear margin, which is why their limit is lower.
FAQ
Chain wear: questions
When should I replace my bike chain?
When wear reaches Park Tool's limit for your drivetrain: 0.5% on 11-speed and up, 0.75% on 10-speed or fewer, 1.0% on a single-speed. A chain checker shows it directly; with a ruler, 24 rivets measuring more than 12 1/16 inches is about 0.52%.
How do you check chain wear with a ruler?
Line a rivet up with the ruler's zero, count 24 more rivets, and read where the last one sits. A new chain is exactly 12 inches. Park Tool's rule: replace it if it's more than 1/16 inch over.
Do I need a new cassette with a new chain?
Not if you replace the chain in time. Running a chain past its wear limit wears the cogs and chainrings too, and a new chain may skip on them — then both need replacing.
Does chain stretch really happen?
Not literally. Park Tool explains that the chain's rivets and rollers wear, which lengthens the pitch and gives "the illusion of stretching."
Something not answered here? Just ask — I’d rather talk it through than have you guess.
Sources
Where these numbers come from
- [1]Park Tool, “When to Replace a Worn Chain” (opens in a new tab)Limits: 1.0% single-speed, 0.75% for 10 speeds or fewer, 0.5% for 11 or more; the 24-rivet ruler method.
- [2]Park Tool CC-4.2 Chain Checker (opens in a new tab)Replace at or just before 1.0%, 0.75% or 0.5% by drivetrain.
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