Three measurements give you the link count, before you cut a single pin.
Chainstay in millimetres, teeth on the biggest chainring, teeth on the biggest cog. This bicycle chain length calculator turns those into links, inches and millimetres, and writes out every step so you can check our arithmetic against your tape.
Chain length from chainstay, chainring and cog
Measure the chainstay from the centre of the bottom bracket spindle to the centre of the rear axle. Not to the dropout tip. Most road frames land between 405 and 420 mm; city bikes run longer, kids' bikes much shorter.
- C, chainstay in inches (mm ÷ 25.4)410 / 25.4 = 16.142 in
- 2 × C32.283 in
- F ÷ 4, largest chainring50 / 4 = 12.50
- R ÷ 4, largest cog32 / 4 = 8.00
- Allowance+ 1 in
- L before rounding53.783 in
- Rounding ruleup to next whole inch
- L after rounding54 in
- Links (L × 2, 1/2 in pitch)54 x 2 = 108
- Chain width to order5.5 mm outer width
Wear limit for 11 speed: replace at 0.5% elongation. Over 12 in of chain that is about 12 1/16 in, pin to pin. A chain past that eats the cassette.
L (in) = 2 × C + F ÷ 4 + R ÷ 4 + 1
C = chainstay mm ÷ 25.4 · F = largest ring · R = largest cog
Round L up to the next whole inch. Links = L × 2.
A starting length, not a cut line. Check it on the bike with the chain over big ring and big cog before you break it.
Send these figures with an inquiryHalf an inch per link, and the teeth do the rest
Every modern bicycle chain has a 1/2 in pitch. One inch of chain is two links, an inner and an outer. That is why the formula works in inches and doubles the answer at the end.
The chain runs the length of the chainstay twice, top run and bottom run. That is the 2C. Then it wraps roughly half of each sprocket. A full turn of a 50 tooth ring is 50 half-inches, or 25 inches; half of that wrap is 12.5 inches, which is the same as 50 divided by 4. Same logic for the cog.
The extra inch on a derailleur bike gives the rear mech enough slack to swing its cage when you shift to the small ring and small cog. Leave it off and the big-big combination can lock the drivetrain or rip the hanger. We see that failure every season, usually after someone sized a replacement 11 speed road bike chain by laying it beside the old one. The old one had stretched.
Single-speed and internal hub bikes have no cage to take up slack. The chain length there is set by the dropout or the eccentric bottom bracket, so the calculator drops the inch, rounds to the nearest even link count and leaves the last few millimetres to the axle position. If you can't get even links to fit, a half link is the fix, not a stretched tensioner.
Five bikes, five link counts
These are the setups that come across the desk most. Run your own numbers above; these are here so you can sanity-check a result that looks wrong.
| Bike | Stay | Ring / cog | Drive | L raw | Links |
|---|---|---|---|---|---|
| Road, compact 50/34, 11-32 | 410 mm | 50 / 32 | Derailleur | 53.78 in | 108 |
| Road, mid-compact 52/36, 11-30 | 405 mm | 52 / 30 | Derailleur | 53.39 in | 108 |
| 1x gravel, 12 speed | 425 mm | 40 / 44 | Derailleur | 55.47 in | 112 |
| City commuter, 8 speed | 440 mm | 38 / 34 | Derailleur | 53.65 in | 108 |
| Kids' 16 in, coaster brake | 300 mm | 28 / 16 | Single-speed | 34.62 in | 70 |
The kids' bike result is 69.2 links before rounding to the nearest even number. Most kids' bikes run a 1/8 in wide single-speed chain; the pitch is still 1/2 in, so the formula holds. See kids' bike parts for widths.
When the chain you have is already too long
Chains don't stretch so much as wear at the pins and rollers. The pitch grows, the chain rides higher on the teeth and starts chewing the cogs. Measure 12 inches of chain, 24 links, pin centre to pin centre.
- New chain, 24 links12 in
- 11 and 12 speed, replace at 0.5%12 1/16 in
- 8 speed and below, replace at 0.75%12 3/32 in
- Check interval, road useevery 1,500 mi
A chain past 0.5% wear eats an 11-speed cassette. Replace it in time and the cassette usually outlives two or three chains. Leave it, and the new chain skips on the worn cogs and you buy both. Our drivetrain page lists the chain widths by speed count, and the cassette freehub standards that go with them.
One thing we won't do: ship a replacement chain without a length figure. If you don't have one, send the three numbers from this calculator and we'll do the sum in the reply.
Got the link count? Send it with the speed count.
Chains on the catalogue start from an indicative $24 with a quick link. The figure in our reply is the one we hold for seven days. Not sure what else to read off the bike? The five compatibility checks cover it.