🔗 Bike Chain Length Calculator
Estimate the chain length needed using the standard bike mechanic's rule-of-thumb formula, based on chainstay length and your largest chainring and cog.
The chainstay formula
The tool uses the mechanic's rule of thumb, sizing the chain from the chainstay and the two largest sprockets:
length (in) = 2 × chainstay + (big chainring + big cog) / 4 + 1
links = length / 0.5, rounded up to the next even numberThe /4 is the wrap - the chain sits on about half the teeth of each
sprocket, and each tooth is half an inch of chain. The +1 covers the
derailleur cage. With the defaults, a 17.7 in chainstay with a 50t ring and 25t
cog, that is 35.4 + 18.75 + 1 = 55.15 in, or 110.3 links, rounding up to
112 links.
Getting the inputs right
- Chainstay is centre of bottom bracket to centre of rear axle: 16.5-17.5 in on most road bikes, 17-18.5 in on mountain bikes. With sliding dropouts, measure where the wheel will actually sit.
- Largest ring and largest cog, even if you never ride that combination - the chain still has to reach it.
- The count is always even because a chain alternates inner and outer plates.
- On full suspension, measure where the travel makes the chainstay longest.
Frequently asked questions
What chain length do I need for a 50t ring and a 25t cog?
On a 17.7 in chainstay, 112 links - 55.15 in of chain rounded up to an even count. New chains ship at 114 or 116 links, so you shorten one to fit.
How long is one chain link?
Half an inch. Bicycle chain is 1/2 in pitch, so 112 links is 56 in. Some brands instead call a full inch a link and the half inch a half link, which is why a 116 link chain and a 58 link chain can be the same part.
Can I copy the length of my old chain?
Yes, if the rings, cassette and derailleur are unchanged. Lay both chains flat side by side and count links rather than measuring inches - a worn chain can be nearly 1% longer than it started.