Bicycle Chain Length Calculator
Enter your bike's chainstay length and the tooth counts of the largest front chainring and rear cassette cog. The calculator applies the industry-standard Park Tool formula to give you the chain length in links and millimetres, rounded up to the nearest even number of links.
mm
teeth
teeth
Rounded up to the nearest even number of links
Convert chainstay to inches
Apply the formula (L in inches)
Convert to links (× 2), round up to nearest even
- 1
Convert chainstay to inches
432 ÷ 25.4 = 17.008 - 2
Chain length formula (inches)
2 × 17.008 + 50 ÷ 4 + 34 ÷ 4 + 1 = 56.016Park Tool formula: 2 × chainstay_in + front_teeth/4 + rear_teeth/4 + 1 - 3
Convert to links (× 2)
56.016 × 2 = 112.03 - 4
Round up to nearest even number of links
ceil(112.03) → even = 114Chains must have an even link count to close with alternating inner/outer plates.
How does this calculator work?
Chain length (inches) = 2 × chainstay_in + front_teeth/4 + rear_teeth/4 + 1. Multiply by 2 for the link count and round up to the nearest even number. A 432 mm chainstay with a 50T front and 34T rear cog gives 112 links (≈1422 mm). Always use the largest chainring and largest rear cog for the calculation.
Formula
How this is calculated
The Park Tool formula estimates the minimum chain length needed to span the largest front chainring and the largest rear cog without going through the rear derailleur. The two factors account for (1) the straight runs of chain between the two sprockets: roughly 2 × the chainstay length (one run on the top, one on the bottom), and (2) the chain wrapped around the teeth on each sprocket: (front teeth + rear teeth) / 4, which approximates the extra length used by partial engagement on each side. Adding 1 inch provides slack for the rear derailleur cage to take up chain under full extension without over-tensioning.
The result in inches is multiplied by 2 to convert to links (since each standard chain link is 0.5 inches or 12.7 mm) and rounded up to the nearest even number, because a chain must alternate inner and outer plates and therefore always has an even total link count. The formula applies to 1× and 2× drivetrains on derailleur bikes; 3× front cranksets may need an additional 1-inch buffer. Fixed-gear, single-speed, and internal-gear hub bikes use a different method (chainstay adjustment slots).
Always measure your actual chainstay length with a tape measure from the centre of the bottom bracket axle to the centre of the rear axle. Cassette and chainring tooth counts are usually printed on the components.
Frequently asked questions
A derailleur chain alternates inner and outer link plates. To close the chain into a loop with a master link or chain pin, both ends must have the same type of plate — which only happens when the total link count is even. Using an outer-outer joining link (a "missing link" or master link) can allow odd counts, but most manufacturers still recommend even counts.
Always use the largest front chainring and the largest rear cog. This ensures the chain is long enough for that gear combination, which places the most demand on chain length. The rear derailleur absorbs the slack in all other (smaller sprocket) combinations.
A chain that is too long will sag, shift poorly in small-small combinations, and risk dropping. Too short, it can damage the derailleur or snap when shifting to big-big. If in doubt, err slightly long by 2 links and check that the derailleur arm angle is within the manufacturer's range in your smallest-smallest gear combination.
TG we-Calculate Editorial Team. (2026). Bicycle Chain Length Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/chain-length-calculator
TG we-Calculate Editorial Team. "Bicycle Chain Length Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/chain-length-calculator.
TG we-Calculate Editorial Team, "Bicycle Chain Length Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/chain-length-calculator
@misc{wecalculate_chain_length_calculator, title = {Bicycle Chain Length Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/chain-length-calculator}}, year = {2026}, note = {TG we-Calculate} }
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