Calculating roller chain length before ordering is one of the most practical skills in industrial maintenance. Getting it wrong by two links means the chain will not close the loop or will require an offset link. The standard formula for a two-sprocket drive is established in ANSI B29.1 and ISO 606.
The Chain Length Formula
The chain length formula calculates the number of links required to form a closed loop from three inputs: centre distance between shaft axes, teeth on the drive sprocket, and teeth on the driven sprocket. Express all dimensions in pitches by dividing the centre distance by the chain pitch.
L = links (round UP to nearest even number)
C = centre distance ÷ chain pitch (in pitches)
N₁ = small sprocket teeth N₂ = large sprocket teeth
Worked Example
ANSI 60 chain (pitch 19.05 mm), 17T drive sprocket, 34T driven sprocket, 500 mm shaft centres.
500 ÷ 19.05 = 26.25 pitches
2C = 52.50 (N₂+N₁)/2 = 25.50 last term = 289 / 1036.6 = 0.279
L = 52.50 + 25.50 + 0.279 = 78.28 links
78.28 → 80 links. Never round down; always round to an even number to avoid needing an offset link.
Why Even Links Are Required
Roller chain alternates inner and outer links. A complete loop must have an even total so the two ends meeting at the connecting link are both inner links. An odd count requires an offset (half) link, which carries only 60 to 80 percent of normal breaking load. A loop that is one link too short cannot close on the sprockets without force.
Converting Links to Physical Length
Physical chain length (mm) = link count × pitch. For the example: 80 × 19.05 = 1,524 mm. Specify both link count and loop circumference when ordering.
Adjusting Centre Distance for a Clean Even Count
If the formula gives an odd result, use the rearranged formula to find the exact centre distance for a specific even link count:
Common ANSI Pitches: Centre Distance in Pitches
| Chain | Pitch (mm) | 500 mm centre (pitches) | 1000 mm centre (pitches) |
|---|---|---|---|
| ANSI 40 | 12.70 | 39.37 | 78.74 |
| ANSI 50 | 15.875 | 31.50 | 62.99 |
| ANSI 60 | 19.05 | 26.25 | 52.49 |
| ANSI 80 | 25.40 | 19.69 | 39.37 |
| ANSI 100 | 31.75 | 15.75 | 31.50 |
| ANSI 120 | 38.10 | 13.12 | 26.25 |
Common Errors
| Error | Consequence | Fix |
|---|---|---|
| Rounding down instead of up | Loop too short to close on sprockets | Always round UP to nearest even number |
| Mixed units (mm and inches together) | Completely incorrect result | Convert all inputs to one unit before applying the formula |
| Not converting centre distance to pitches | Physically meaningless result | Divide centre distance by chain pitch first |
| Accepting an odd link count | Requires offset link — reduces breaking load 20 to 40 percent | Adjust centre distance or add one link |
EverPower Roller Chains Australia supplies ANSI roller chain in any link count. Our Sydney team can verify your calculation before supply. Call +61 2 9708 3322 or email [email protected].
+61 2 9708 3322 | [email protected] | 27 Harley Crescent, Condell Park NSW 2201