Chain Length Calculator
For a bike, enter chainstay length and the largest chainring and cog to get the chain length in links and how many links to remove from a new chain. For a roller or motorcycle chain drive, enter both sprockets, the chain size and the center distance to get the link count and corrected center distance.
A derailleur bike chain should wrap the largest chainring and the largest cog, bypassing the rear derailleur, plus 2 links (one inch) — the Shimano and SRAM "big-big + 2" rule.
Use the Chain Length Calculator
Bike chain length — how many links?
Chainstay = centre of the bottom bracket to the centre of the rear axle. Use the largest chainring and the largest cog.
Check on the bike: in big ring + big cog the chain must not be taut; in small ring + small cog the derailleur cage must not fold back. SRAM Eagle Transmission uses SRAM's chain length chart instead.
Roller chain drive — links and center distance
Drive Parameters
Common: 0.25 (#25), 0.375 (#35), 0.5 (#40), 0.625 (#50), 0.75 (#60)
Chain Drive Diagram
Fill in the parameters and click Calculate to see results.
Chain sizes and pitch
For ANSI and motorcycle chains the first digit (or digits) is the pitch in eighths of an inch: #40 = 4/8 in, 520 = 5/8 in. Bicycle chains are all ½-inch pitch.
| Chain | Pitch (in) | Pitch (mm) | Typical use |
|---|---|---|---|
| Bicycle chain (½ in) | 0.5 | 12.7 | Derailleur 3/32 in and single-speed 1/8 in bicycle chains |
| ANSI #25 | 0.25 | 6.35 | Light drives, scooters, small go-karts |
| ANSI #35 | 0.375 | 9.525 | Mini bikes, go-karts, light machinery |
| ANSI #40 / #41 | 0.5 | 12.7 | Go-karts, conveyors, general machinery |
| ANSI #50 | 0.625 | 15.875 | Heavier machinery, go-kart racing |
| ANSI #60 | 0.75 | 19.05 | Agricultural and industrial drives |
| ANSI #80 | 1 | 25.4 | Heavy industrial drives |
| ANSI #100 | 1.25 | 31.75 | Heavy industrial drives |
| Motorcycle 415 / 420 / 428 | 0.5 | 12.7 | Pit bikes, small motorcycles and ATVs |
| Motorcycle 520 / 525 / 530 | 0.625 | 15.875 | Most street and dirt motorcycles |
| Motorcycle 630 | 0.75 | 19.05 | Older large motorcycles |
| ISO 06B | 0.375 | 9.525 | European roller chain, 9.525 mm |
| ISO 08B | 0.5 | 12.7 | European roller chain, 12.7 mm |
| ISO 10B | 0.625 | 15.875 | European roller chain, 15.875 mm |
| ISO 12B | 0.75 | 19.05 | European roller chain, 19.05 mm |
Quick answer
A derailleur bike chain should wrap the largest chainring and the largest cog, bypassing the rear derailleur, plus 2 links (one inch) — the Shimano and SRAM "big-big + 2" rule. The Park Tool formula estimates it in inches: L = 2C + F/4 + R/4 + 1, where C is the chainstay length in inches, F the largest chainring and R the largest cog; each inch is 2 links. Example: 16.5 in chainstay, 52T ring, 28T cog → 33 + 13 + 7 + 1 = 54 in = 108 links, while the exact big-big wrap (106.4 links, closed at 108) + 2 gives 110 links. For any roller chain drive, links = (N1 + N2)/2 + 2C/p + ((N2 − N1)/2π)²·p/C, rounded up to an even number.
Examples
| Chainstay | Largest ring / cog | Formula 2C + F/4 + R/4 + 1 | Big-big + 2 links |
|---|---|---|---|
| 16.5 in (419 mm) | 50T / 28T | 53.5 → 54 in = 108 links | 108 links |
| 16.5 in (419 mm) | 52T / 28T | 54 in = 108 links | 110 links |
| 17.25 in (438 mm) | 50T / 28T | 55 in = 110 links | 112 links |
| 17.25 in (438 mm) | 34T / 50T | 56.5 → 57 in = 114 links | 114 links |
| 17.5 in (445 mm) | 32T / 52T | 57 in = 114 links | 116 links |
Enter your chainstay length and largest chainring and cog to get the links to keep and to cut.
Summary
Two calculators in one. The bicycle calculator takes the chainstay length (bottom bracket centre to rear axle) and the tooth counts of the largest chainring and largest cog, wraps a half-inch-pitch chain around them exactly, and adds the 2 links Shimano and SRAM specify for derailleur bikes. It also shows the Park Tool estimate 2C + F/4 + R/4 + 1 inches and how many links to remove from a new 112- to 138-link chain. The roller chain calculator uses the standard ANSI/ISO formula for two sprockets, with presets for ANSI #25 to #100, motorcycle 415 to 630 and ISO 06B to 12B chains, and returns the even link count, chain length and corrected center distance.
How it works
- Bike: measure the chainstay from the centre of the bottom bracket to the centre of the rear axle, and count the teeth on the largest chainring and the largest cog.
- The calculator wraps a ½-inch chain around those two sprockets with the roller chain formula, rounds up to a closable even number of links and adds 2 links for the rear derailleur.
- It also shows the Park Tool estimate L = 2C + F/4 + R/4 + 1 inches (1 inch = 2 links) and the links to remove from the new chain you bought.
- Roller chain: pick the chain size (ANSI, motorcycle or ISO), enter both sprocket tooth counts and the center distance.
- The tool applies L = (N1 + N2)/2 + 2C/p + ((N2 − N1)/2π)²·p/C, rounds up to an even link count and gives the corrected center distance for that chain.
Use cases
- Cutting a new road, gravel or mountain bike chain to the right number of links.
- Checking chain length after changing to a bigger cassette or chainring.
- Sizing a single-speed or fixed-gear chain.
- Ordering the right link count for a motorcycle, ATV or go-kart chain (420, 428, 520, 530).
- Designing a conveyor or machine drive with ANSI roller chain and setting the shaft spacing.