Chain length calculator

A new bicycle chain is deliberately supplied too long (usually 114 to 138 links). Before fitting, you shorten it to the right length for your bike. Too long gives you a slack chain and poor shifting; too short can damage the derailleur if you shift into big-big. With the calculator above you'll know in one go how many links you need.

How does the calculation work?

We use the method that Park Tool and Sheldon Brown also follow. Chain length depends on three measurements: the largest chainring (F, teeth), the largest sprocket on the cassette (R, teeth) and the chainstay length (C, centre of the bottom bracket to centre of the rear axle).

Formula (big-big + 2): length in inches = 2 × C + F ÷ 4 + R ÷ 4 + 1. Every inch is 2 links, and you round up to an even number. That extra inch (2 links) is the slack the derailleur needs. On a full-suspension mountain bike, add another 2 links for the rear suspension travel.

Rigorous formula: for big differences between chainring and sprocket (for example 50 at the front and 11 at the back), we add the term (F − R)² ÷ (16π² × C). In practice it makes at most 1 link of difference, but for 1x drivetrains with large cassettes it's the most accurate method.

How to measure the chainstay

Measure from the centre of the bottom bracket to the centre of the rear axle, in millimetres. On road bikes this is usually 405–415 mm, on gravel bikes 420–440 mm and on mountain bikes 425–450 mm. The exact value is in your bike's geometry chart.

Worked example

Road bike with 50/34 chainrings, an 11-34 cassette and a 410 mm chainstay (16.14 inches): 2 × 16.14 + 50 ÷ 4 + 34 ÷ 4 + 1 = 54.3 inches → 109 links, rounded up to an even number: 110 links.

Check after shortening

Shift into big-big: the derailleur cage should still have a little play. Then shift into small-small: the chain mustn't hang slack against the derailleur. If both check out, the length is right. Always use the supplied quick link to close the chain; shorten the chain with a chain tool.

Frequently asked questions

Can I just measure my old chain? Yes, if the old chain was the right length. Lay both chains side by side and count the links. Note: a worn chain has stretched, so count links rather than measuring centimetres.

Do waxed chains need the same length? Yes. Waxing doesn't change the length at all. Our waxed chains come with enough links and a quick link, so you can size them straight away.

Even or odd number of links? Always even. A chain is made up of alternating inner and outer links; with a quick link you join two inner links together.