Chain Length Calculator
Size a bicycle chain with the Park Tool equation. Enter the chainstay length (inches, cm, or mm), the teeth on your largest chainring, and the teeth on your largest rear cog to get the chain length in inches and links.
Example: with Chainstay length 16.5 · Chainstay unit inches · Largest chainring (teeth) 50 · Largest rear cog (teeth) 28 → Chain length: 54 in (rounded up).
- Number of links108 links
- Exact formula value53.5 in (exact)
Computed by the calculator below using its default values. Change any input to see your own numbers.
Park Tool equation: length (in) = 2 × chainstay + (front teeth ÷ 4) + (rear teeth ÷ 4) + 1, rounded up to an even number of half-inch links.
How the equation sizes a chain
A chain has to wrap the largest chainring and largest cog at the same time with enough length for the derailleur to take up slack in the small-small combination. The Park Tool equation captures that: twice the chainstay length sets the basic loop, a quarter of each of the big gears accounts for wrapping them, and the extra inch adds derailleur clearance. The result is rounded up to an even number of half-inch links because a chain can only be joined at whole links.
This equation method is precise when you know your chainstay length. An alternative shop method skips the math: wrap the chain around the big ring and big cog without routing through the derailleur, then add one inch (two links). Both should land within a link of each other.
How it’s calculated
Length in inches = 2 × chainstay (in) + largest chainring teeth ÷ 4 + largest rear cog teeth ÷ 4 + 1. Centimeters convert at 2.54 per inch and millimeters at 25.4. Links = length × 2 (half-inch pitch), rounded up to the next even number; reported length = links ÷ 2.
Standard 1/2-inch chain pitch and a rear derailleur with typical capacity; single-speed, tensioned, and gearbox setups follow different rules.
Example chain lengths by setup
| Setup | Chainstay | Big ring / cog | Chain length |
|---|---|---|---|
| Road | 16.5 in | 50T / 28T | 54 in (108 links) |
| Gravel | 16.9 in | 48T / 36T | 56 in (112 links) |
| MTB 1x | 17.3 in | 34T / 52T | 58 in (116 links) |
| Single-speed | 16.0 in | 48T / 16T | 49 in (98 links) |
Computed with the Park Tool equation, rounded up to an even link count. Chain pitch 1/2 inch.
Common mistakes
- Using the small chainring or cog instead of the largest ones — the chain must fit the big-big wrap.
- Measuring wheelbase or top tube instead of the chainstay (rear axle to bottom bracket).
- Forgetting to round up to an even link count; a chain only joins at whole links.
Frequently asked questions
What is the bike chain length formula?
Length in inches = 2 × chainstay length + (largest chainring teeth ÷ 4) + (largest rear cog teeth ÷ 4) + 1, then round up to an even number of links.
How do I measure chainstay length?
Measure the straight-line distance from the center of the rear axle to the center of the bottom bracket. That is the chainstay length the equation uses.
How many links should my chain have?
Multiply the inch result by two, since each half-inch pitch is one link, then round up to an even number. A 54-inch chain is 108 links.
What about single-speed bikes?
Single-speeds use a fixed chainstay and no derailleur slack, so length is set by exact wheel position. Size it so the wheel sits mid-dropout with proper tension, then remove links to fit.