Chain Length Calculator

For a replacement, you need the correct number of links for your bike and drivetrain. For wear, you measure how much the distance between pins has increased. A wear checker cannot tell you where to cut a new chain, and a chainstay measurement cannot tell you whether the old chain is worn. For related drivetrain setup, see our gear ratio calculator and crank length calculator.

To check wear with a ruler, gently tension a straight chain section. Measure from one pin's center across 24 pin-to-pin intervals to the 25th pin. An unworn half-inch-pitch chain spans 12 inches (304.8 mm). Readings near a replacement threshold need a checker approved for that chain; follow the chain maker's limit. See our chain wear and replacement guide for gauge choice and replacement decisions.

The traditional geometric model produces a length in inches. The tool rounds that estimate up to a whole inch, then multiplies by two to return half-inch links. For example, 410 mm chainstays with a 50-tooth chainring and 28-tooth cog produce about 52.783 inches before rounding: 53 inches, or 106 half-inch links (134.62 cm).

That example checks the units, not whether 106 links is the right cut length for a particular drivetrain. The model's fixed allowance does not replace system-specific sizing. Do not add a separate connector allowance to this estimate; use the manufacturer's complete sizing procedure instead.

On a conventional half-inch-pitch bicycle chain, adjacent pins are 12.7 mm apart. One inner link plus one outer link spans 25.4 mm (one inch), sometimes called a full link. A chain sold as 116 links counts 116 half-inch pitches, not 116 one-inch pairs. Its nominal closed-loop length is 58 inches.

1. Only copy an old link count if its sizing was correct and the drivetrain and frame setup have not changed.
2. Mark a starting link and count each inner and outer link once. If comparing chains side by side, match inner to inner and outer to outer, pin by pin, rather than matching end positions.
3. Include the connector in the finished count. A conventional quick link replaces one outer link, one half-inch pitch, not an inner-and-outer pair. Follow the manual's diagram to avoid counting it twice.

Park Tool's sizing guide shows the pin-by-pin comparison. If the old sizing is unknown, use the manufacturer's procedure from scratch.

There is no universal “add two links” rule. Identify the rear derailleur model, chain model, cassette and chainring before cutting. For Shimano, find that derailleur in Shimano's technical documents and follow its chain-length diagrams, including the connector and chain-end arrangement. Do not apply a different generation's link allowance.

SRAM's Eagle Transmission guide specifies a bike-model and chainring-based chain length, Setup Key position and Setup Cog through its official chain length guide. That is not interchangeable with conventional Eagle or road Flattop sizing. Use the relevant SRAM chain manual for those systems.

On full-suspension bikes, chainstay distance can change through travel. Use the frame and drivetrain makers' specified suspension position and procedure, not a generic fully extended, compressed or sag position. If the instructions require shock removal or a procedure you cannot safely perform, ask a shop. Single-speed and fixed-gear bikes need their own tensioning instructions.

A worn chain accelerates cassette and chainring wear, leading to expensive drivetrain replacements. Use a chain wear checker tool regularly, using a gauge and replacement limit specified for your chain. Roller dimensions and wear limits differ between systems; speed alone is not enough to choose a checker or threshold.

Wear lengthens the spacing between pins but does not add links. You can copy a verified correct link count, but not the old chain's stretched end-to-end length. For dropped, broken, stiff or skipping chains, use the chain repair decision tree before replacing parts.