Chain is procured by pitch, strand count, and total link count — or as cut length for some supplier formats. Incorrect length causes impossible installation, excessive slack, or tension too tight for adjustment. For breakdown maintenance, counting links on the removed chain is the most reliable method; for new drives or modified centre distances, the standard length formula applies with rounding to an even number of links.
Quick replacement — count links on old chain
The fastest and most accurate method for like-for-like replacement: remove the chain, lay flat, and count outer links (or inner links — be consistent). Total links must be even for standard connecting link assembly on most roller chain.
Confirm pitch and strand count from link plate stamping before ordering. A length match on the wrong pitch is useless.
If the old chain was shortened in the past with an extra connecting link or removed links, counting alone may perpetuate a non-standard length — compare to calculated length if centre distance is known.
- Count all links including connecting link
- Verify even link count — odd counts need half-link or special solution
- Note connecting link type: spring clip, cotter pin, riveted endless
- Order same pitch and strand designation
Standard length formula (new drives)
For drives with known centre distance (C) in pitches, sprocket teeth N1 (driver) and N2 (driven), and pitch P in mm, the approximate number of links (L) follows the industry formula accounting for wrap on both sprockets.
In practice, suppliers and maintenance teams use: L = (2C/P) + (N1 + N2)/2 + K, where K is a small constant depending on wrap (often 0 to 2 links adjustment), then round to nearest even integer.
Always round to even link count. If calculation falls on odd, round up or down based on whether slight slack or slight tension is preferable — most drives prefer the next even number that avoids over-tight installation.
| Symbol | Meaning | Units |
|---|---|---|
| P | Chain pitch | mm |
| C | Centre distance between sprocket centres | mm |
| N1 | Teeth on driver sprocket | count |
| N2 | Teeth on driven sprocket | count |
| L | Total links (must be even) | links |
Worked example
Example: 08B-1 chain, pitch P = 12.7 mm, centre distance C = 500 mm, driver N1 = 19 teeth, driven N2 = 57 teeth.
Convert centre to pitches: 2C/P = 1000 / 12.7 ≈ 78.74 pitches. Add (19 + 57)/2 = 38. Sum ≈ 116.74 links before rounding. Round to 116 or 118 links (even) — confirm with supplier chart or engineering for exact K factor.
Send teeth counts, centre distance, and pitch on RFQ when length is critical — we will confirm link count before cutting or shipping.
Centre distance measurement tips
Measure centre distance between sprocket pitch circles, not outer hub diameters. On installed drives, measure shaft centre to shaft centre if sprockets are same diameter; otherwise use geometry or reference original drawing.
Adjustable drives (motor slides, tensioners) should be set to normal operating position before measuring — not fully tightened or fully loose.
Record whether measurement is shaft-to-shaft or pitch-line-to-pitch-line — confusion here causes systematic length errors.
Even links, half links, and endless chain
Standard roller chain uses even link counts with a connecting link joining two inner ends. Odd link counts require a half-link (offset link), which reduces strength and should be avoided on heavy drives if possible.
Endless chain ( riveted at factory) suits applications where connecting link clearance is problematic or contamination enters at the joint. Specify endless at order — field riveting needs proper tooling.
Connecting links: spring clip types allow faster assembly but clip must face away from travel direction on some safety-critical drives; cotter pin types suit higher reliability preferences.
Tension adjustment and length margin
Motor slide bases and adjustable tensioners absorb some length tolerance. If the drive has no adjustment, chain length must be exact within one link — there is no field stretch allowance on new chain.
When replacing on a fixed centre distance, compare calculated length to old chain count. Discrepancy often reveals previous field modification or measurement error on original install.
After installation, correct sag on the slack span is typically 1–2% of centre distance for horizontal drives — see lubrication and maintenance guide for tension setting.
Multi-strand and long-span conveyors
Duplex and triplex chain use the same length calculation — strand count does not change link count, only chain width.
Long conveyor runs may use multiple sections with connecting links at floor levels. Document link counts per section for partial replacement without full line shutdown.
Elevated temperature or heavy load may require slight length check after first 48 hours running — settle and wear-in can change effective tension.
Common mistakes to avoid
- Ordering by overall length in mm without specifying pitch and link count
- Odd link count without ordering half-link
- Measuring worn elongated chain and ordering same link count for fixed centre distance — new chain will be too long
- Forgetting connecting link in count on old chain with multiple joints
- Using centre distance measured with chain installed under tension
- Mixing formula for roller chain with leaf chain or conveyor chain formulas
RFQ checklist
- Chain pitch and strand count (from stamping or measurement)
- Link count from old chain OR centre distance + both teeth counts
- Even link count confirmed
- Connecting link type or endless requirement
- Adjustment method on drive (fixed vs motor slide)
- Application: horizontal, inclined, vertical (elevator)
- Photos of existing chain tag or drive layout if uncertain