Chain Length Calculator
Enter both sprocket tooth counts, center distance and chain pitch to get the exact chain length — rounded to an even link count to avoid offset links.
Last updated: 2026-09-15
How the calculation works
- The classical chain equation wraps straight spans plus arc contact on each sprocket, expressed in pitches.
- The result rounds UP to the nearest even pitch count — even counts use a standard connecting link instead of a weaker offset link.
- Pitch conversions for ANSI sizes (#25–#60) are built in.
Formula
L(pitches) = 2C/p + (T₁+T₂)/2 + p(T₂−T₁)²/(4π²C)
| Symbol | Meaning | Unit |
|---|---|---|
L | Chain length | pitches |
C | Center distance | mm |
T₁, T₂ | Sprocket teeth | — |
p | Chain pitch | mm |
Worked example
17T and 34T sprockets at 400 mm with #40 chain (12.7 mm): L = 63.0 + 25.5 + 0.03 ≈ 88.5 → order 90 pitches (1,143 mm). The offset link would have been needed at 89 — the even 90 avoids it.
Interpreting the result
Chain drives wear by pitch elongation: a 'stretched' chain rides higher on sprocket teeth and eventually jumps. Order two links extra with a tensioner, or set center distance adjustable by ±2 pitches. Never reuse an offset link in a power drive — it's the weak point.
Assumptions
- Standard roller chain, two-sprocket drive, no idlers.
- Slight chain tension at installation.
Limitations
- Idler sprockets and serpentine paths add length segments — measure those separately.
- Chain sag in long horizontal spans needs a catenary allowance.
Frequently asked questions
How do I measure chain pitch?
Center-to-center distance of three consecutive pins, divided by two. 12.7 mm = #40 chain.
Why even number of links?
An even count closes with a spring-clip connecting link (full strength). Odd counts need an offset link — two pins on a bent side plate, roughly 20–30% weaker.