Chain Pitch Converter

Roller chain is identified by ANSI chain number.

Chain numbering system:

• First digit(s) = pitch in 1/8 inch increments
• Last digit: 0 = standard, 1 = lightweight, 5 = bushing

Example: Chain #40 = 4/8 inch = 0.5 inch pitch

Common chain sizes:

Double-strand chains (e.g., #40-2) have roughly 1.7x the tensile strength.

Tensile is not what you design to. The figures above are the load that breaks a new chain in a pull test. Standard practice is a safety factor of 6 to 8, so a #40 chain rated 3,125 lbs is good for roughly 390 to 520 lbs of steady working load. Run closer than that and the pins gall, the chain elongates fast, and it starts skipping teeth long before anything snaps. Shock loads, reversing drives, and dirty conditions push you toward 8 rather than 6.

A note on #25 and #35: both are bushed chains with no rollers at all. The bushing takes the tooth contact directly. The width column still applies, it is just bushing width rather than roller width, and it is why those two sizes wear faster than a rollered chain of the same pitch under the same load.

Pin diameter is what you measure when a chain has no markings left on it. Pitch and pin together identify a chain unambiguously, which is why both are listed here. The ISO column is the same chain under the European designation, useful when a parts catalogue lists 08A-1 where the machine’s manual says #40.

Pitch is the single most important number when matching a chain to its sprockets, because the teeth have to line up exactly with the links. A chain and sprocket of different pitch won’t mesh, no matter how close the sizes look, which is why replacement parts are specified by pitch first.

Bicycle chains are a special case worth knowing: almost all modern bikes use a 1/2-inch pitch, so what separates a 7-speed chain from a 12-speed one isn’t pitch at all, it’s width. More sprockets packed into the same space means narrower chains and tighter spacing. Industrial and motorcycle roller chains, by contrast, come in the ANSI pitches above, where both the pitch and the roller size change between standards. One practical tip: a chain “stretches” as it wears (the pivots wear, not the steel), so a worn chain measures slightly longer than its nominal pitch and should be replaced before it chews up the sprockets.

Motorcycle chain numbers work the same way at the front and differently at the back. In 520, 525 and 530 the leading 5 is still the pitch in eighths, so all three are 5/8 inch (15.875 mm) and share the pitch of #50 above. The remaining two digits are a width code rather than a clean fraction: 520 measures 1/4 inch between the inner plates, 525 about 5/16, and 530 about 3/8. A 420 or 428 has a 1/2 inch pitch, matching #40, with 420 the narrower of the two. This is why going from a 520 to a 525 needs no sprocket change (same pitch, wider rollers) while going from a 520 to a 428 needs new sprockets front and rear.