Bicycle Chain Length Calculator
Enter your chainstay length and the tooth counts for your largest front chainring and largest rear cog. The calculator returns chain length in links, inches, and millimetres using both the quick Park Tool simple formula and the more precise rigorous formula. Switch between metric (mm) and imperial (inches) input and see a step-by-step breakdown of the math.
Formula
Worked example
Road bike: chainstay 430 mm (16.93 in), 50-tooth front chainring, 34-tooth rear cog. Rigorous: offset = 0.0796 x (50-34) = 1.274; inner = 16.93^2 + 1.274^2 = 288.23; 2*sqrt(288.23) = 33.99; gear term = (50+34)/4 = 21; L = 54.99 in; raw links = 54.99/0.5 = 109.97; round up to next even = 110 links.
How bicycle chain length is measured
Bicycle chains are measured in links, where each link is 0.5 inch (12.7 mm) of pitch. A full link consists of an inner plate pair and an outer plate pair joined together, so chain length must always be an even number to allow the master link (also called a connecting link) to pair an inner plate with an outer plate. Standard road chains come in 116 or 126-link lengths that you shorten to your bike by removing links; you never add links to a new chain.
Simple vs rigorous formula
The Park Tool simple formula (L = 2C + F/4 + R/4 + 1) is a fast approximation that works well when the chainstay is 15 inches (381 mm) or longer and the difference between the largest front and rear cogs is not extreme. It can overestimate length slightly, so the chain will always shift properly but may cause a small amount of droop. The rigorous formula accounts for the actual geometry of the drive triangle and gives a closer result, especially for bikes with short chainstays (cyclocross, BMX, some gravel bikes) or large cog-count spreads (1x drivetrains with a 50-tooth rear cog). Both formulas require only three inputs: chainstay length and the two largest cog sizes.
What measurements do you need?
Chainstay length: measure with a ruler or vernier caliper from the exact centre of the bottom bracket shell (where the crank axle runs) to the exact centre of the rear axle (or hub axle). Do not measure to the dropout face. Typical road bikes are 405-435 mm; MTBs are 415-460 mm; cargo and utility bikes can be 465-520 mm. Largest front chainring: count the teeth on the outermost ring of a double or triple crankset, or the single ring on a 1x drivetrain. Largest rear cog: count the teeth on the biggest sprocket on your cassette, the one used for the easiest climbing gear.
How to verify chain length on the bike
After calculating, confirm the result physically. Route the new chain around the largest front chainring and the largest rear cog without threading it through the derailleur. Pull both ends together until there is no slack. At that joining point, add exactly one complete link (one inner and one outer plate) and fit the master link. This manual check catches any measurement errors and is recommended by Park Tool and Shimano before cutting the chain. If the chain is too long, derailleur tension will bottom out on the smallest cog; if it is too short, the derailleur will over-extend and may be pulled off or bent when shifting to the largest cog.
Typical chain lengths by bike type
| Bike Type | Typical Links | Drivetrain |
|---|---|---|
| Track / fixie | 96-100 | Single-speed, no derailleur |
| Road (compact double) | 106-112 | 50/34 front, 11-28 rear |
| Road (standard double) | 108-114 | 53/39 front, 11-28 rear |
| Gravel / endurance | 110-116 | 48/32 or 1x front, 10-42 rear |
| Cross-country MTB | 114-118 | 1x or 2x, 10-42 rear |
| Trail / enduro MTB | 116-122 | 1x, 10-50 or 10-52 rear |
| Hybrid / commuter | 114-120 | 2x or 3x, 11-34 rear |
| Cargo / e-bike | 120-128 | 1x or 2x, extended chainstay |
These ranges reflect common setups. Your actual count depends on chainstay length and tooth counts.
Frequently asked questions
Should I use the simple or rigorous formula?
Use the rigorous formula as your default - it accounts for the actual geometry of the drivetrain triangle and gives a more accurate result for any chainstay length. The simple formula is a quick approximation that works reasonably well for road bikes with chainstays of 381 mm (15 in) or more, but it can overestimate length by 1-2 links on bikes with short chainstays or wide gear ranges.
Why does chain length have to be an even number?
Each link on a bicycle chain consists of alternating inner and outer plate pairs. The master link (connecting link) joins an inner plate to an outer plate, which means the two ends of the chain must be of opposite types. An even total link count guarantees that. If you end up with an odd number after the calculation, always round up to the next even number - never down.
What chainstay length should I use?
Measure from the exact centre of the bottom bracket axle to the exact centre of the rear wheel axle. The bottom bracket centre is at the mid-point of the shell where the crank passes through the frame; the rear axle centre is in the middle of the quick-release or thru-axle. Measure both sides if possible and average them. A digital vernier caliper or a steel rule gives the best accuracy. Avoid measuring to the dropout slot edge or the end of the chain stay tube.
Do I use the smallest or largest cog for chain length?
Always use the LARGEST rear cog and the LARGEST front chainring. This is the gear combination that creates the longest required chain path. A chain sized for the largest cog will shift correctly through all other gears. Sizing for a smaller cog risks the chain being too short to reach the largest cog without over-extending the rear derailleur.
How many links does a standard new chain have?
Most 10-, 11-, and 12-speed chains are sold in 126-link lengths. Some brands sell 116-link chains aimed at road bikes. You shorten the chain to your calculated length by removing links from one end, then fit the master link. Never lengthen a chain by adding links from an old chain - the wear profiles will differ and shifting will be rough.
Does chain speed (6, 7, 8, 9, 10, 11, 12-speed) affect chain length?
Chain speed (the number of cogs on the cassette) affects chain WIDTH, not length. Narrower chains are required for 11- and 12-speed cassettes so the chain can sit on thinner cog spacing, but the length formula and the 0.5-inch link pitch are identical across all modern derailleur chains. The same calculation works for any speed group.