Estimate bicycle chain length in links from chainstay length and the largest chainring and cog teeth, or find how many links to remove from a new chain.
Bicycle Chain Length Formula
- CL is the modeled chain path length before even-link rounding (inches)
- C is the chainstay length (inches), measured from the center of the bottom bracket to the center of the rear axle
- F is the number of teeth on the largest front chainring
- R is the number of teeth on the largest rear cog
The first equation is a conventional derailleur planning estimate with a selected 1-inch allowance. The alternative estimate adds 2 inches. These are assumptions, not universal rules selected by cog size: exact sizing varies by chain, derailleur, frame, connector and suspension layout. Verify the manufacturer’s current physical sizing procedure before cutting.
The second equation is an idealized two-circle tangent model with no derailleur allowance. It uses circles of circumference tooth count multiplied by half-inch pitch; actual sprocket pitch radii and the polygonal roller-chain path differ. It requires C > |d|. The calculator uses it for the single-speed/fixed-gear estimate and reports the modeled circular path in derailleur modes. It does not establish actual chain fit or available axle adjustment.
Chain length in inches then converts to links. Each link spans a half inch of pitch, so the calculator divides CL by 0.5 and rounds up to the next even number, for a conventional alternating inner/outer chain including its connector. Special half-links and manufacturer-specific counting procedures require separate checks. The compare function subtracts your required link count from the as-sold link count of a new chain and reports how many links to remove before installation.
Typical Chainstay Lengths and New Chain Sizes
If you cannot measure the chainstay directly, the table below gives typical ranges by bike type. Use it to sanity check your measurement or to get a working estimate, then measure before you make the final cut.
| Bike type | Typical chainstay (in) | Typical chainstay (mm) |
|---|---|---|
| Road race | 15.7 to 16.3 | 400 to 415 |
| Endurance road | 16.1 to 16.5 | 410 to 420 |
| Gravel | 16.5 to 17.5 | 420 to 445 |
| Cross-country MTB | 16.9 to 17.3 | 430 to 440 |
| Trail and enduro MTB | 17.0 to 17.7 | 432 to 450 |
| Touring | 17.3 to 18.1 | 440 to 460 |
| Track and fixed gear | 14.8 to 15.6 | 375 to 395 |
| BMX (20-inch wheels) | 12.8 to 13.8 | 325 to 350 |
New-chain packaged lengths vary by exact model and drivetrain, and some bikes need a longer chain. The table below lists typical link counts as packaged, which is the number the calculator compares against when it tells you how many links to remove.
| Drivetrain | Typical as-sold length |
|---|---|
| Shimano 9, 10, and 11 speed (road and MTB) | 116 links |
| Shimano 12 speed MTB | 126 links |
| SRAM Eagle 12 speed MTB | 126 links |
| SRAM road AXS 12 speed | 120 links |
| KMC 8 to 12 speed | 114 to 118 links |
| Single speed and BMX (1/8 inch) | 112 links |
Check the packaging for the exact count before cutting, since manufacturers change lengths between chain models.
Example Problems
Example 1: road bike with a derailleur. The chainstay measures 16.25 inches, the largest chainring has 50 teeth, and the largest cog has 30 teeth. Applying the formula gives CL = 2(16.25) + 50/4 + 30/4 + 1 = 32.5 + 12.5 + 7.5 + 1 = 53.5 inches. Dividing by 0.5 gives 107 links, which rounds up to the next even number, 108 links, or 54 inches of chain. If you bought a 116 link chain, you would remove 8 links before installing it.
Example 2: single speed bike. For C = 15 inches, F = 44 and R = 16, d = 28/(4*pi) and the idealized circular model gives about 45.331595 inches. Even-link rounding gives 92 half-inch links, or 46 inches. Actual sprocket geometry, axle adjustment, tension and connector requirements must still be verified; rounding does not guarantee a usable fit.
Frequently Asked Questions
What happens if my chain is too long or too short? A chain that is too long sags in the smallest gear combinations, shifts sluggishly, and can slap the frame or drop off the chainring on rough ground. A chain that is too short is worse: in the largest ring and largest cog it stretches the rear derailleur past its capacity, which can tear the derailleur off its hanger, bend the hanger, or snap the chain under load. If the estimate falls between sizes, follow the exact manufacturer method and verify every gear combination; derailleur capacity and chain growth constrain both longer and shorter choices.
Do I count the master link in the total? Yes. The master link, or quick link, replaces a normal outer link, so it counts as one link in the final total. When cutting the chain, break it so both ends finish in inner plates; then the quick link supplies the last outer link. If you are comparing against an old chain, snap the master link into the new chain first so you are matching complete lengths.
How do I size a chain for a full-suspension mountain bike? Use the manufacturer-specified position of greatest chain growth and its drivetrain/chain sizing instructions. Greatest growth is not universally at full compression, especially with idlers or unusual suspension paths. Follow the frame maker’s safe procedure for checking travel and the chain maker’s connection instructions before riding.
