Bike chain wear calculator.

Worked example

A new chain measures exactly 12 in over 12 complete links (24 half-links). A 10-speed chain that reads 12 1/16 in (12.0625 in) is 0.0625 ÷ 12 = 0.52% worn. That is under Park Tool’s 0.75% limit for 5 to 10 speed, but at the 1/16 in point Sheldon Brown says to replace the chain. An 11 or 12 speed chain at the same reading is past Park Tool’s 0.5% limit. At 12 1/8 in the chain is 1.04% worn, which Sheldon Brown calls too long to leave: the sprockets will be badly worn.

How it works

Wear % = (measured − 12 in) ÷ 12 in × 100. Place the ruler against one pin and read the pin 12 complete links along, with the chain under slight tension. The replacement points are Park Tool’s: at or just before 0.75% for 5 to 10 speed chains and 0.5% for 11 to 12 speed chains. Sheldon Brown’s ruler guidance is 1/16 in past (0.52%) to replace the chain before the sprockets are damaged, and 1/8 in past (1.04%) as too late. Different makers use different limits, so the tool shows the Park Tool limit for your speed and flags the stricter ruler rule as approaching.

Sources

Retrieved 2026-10-16. Park Tool gives the 0.75% and 0.5% limits; Sheldon Brown gives the ruler method and the 1/16 in and 1/8 in points. The percentages are the simple ratios 0.0625/12 and 0.125/12.

• Park Tool, Chain Wear Indicator CC-3.2 (0.75% and 0.5% limits)
• Sheldon Brown, Chain Wear (12 inch ruler method, 1/16 in and 1/8 in)

FAQ

How do I measure bike chain wear with a ruler?

Line up the zero of a ruler with the centre of one pin, then look at the pin 12 complete links away. A new chain lines up at 12 in; 12 1/16 in is about 0.5% stretch.

When should I replace my bike chain?

Park Tool says to replace 5 to 10 speed chains at or just before 0.75% wear and 11 to 12 speed chains at or just before 0.5%. Sheldon Brown advises replacing at 1/16 in over 12 in, about 0.52%, to protect the sprockets.

What percent chain wear is too much?

At about 1% (1/8 in over 12 in) the sprockets are likely badly worn too, and a new chain may skip on them.

Why is chain wear measured over 12 links?

Twelve complete links is 24 half-links, a length of exactly 12 in on a new chain, so the stretch shows up as a small excess that is easy to read.

Is a chain checker better than a ruler?

A checker such as Park Tool’s CC-3.2 reads against set limits quickly. A ruler can read any value, but is harder to read exactly. Either is fine if used carefully.