Determining chain sizes is a function of learning how to measure
a bicycle chain width, both internal and external, and the bicycle
chain pitch. These three elements together describe a bicycle
chain size and give you the information you need to buy a new
1. How to measure bicycle chain width? INTERNAL
There are 1/8" (3.175mm) and 3/32" (2.38mm) width bicycle
chain. Sizes refer to the distance between the two inner plates.
This is often referred to as the bicycle chain tooth size, since
it predetermines the size or thickness of the teeth on the cogs
or chainrings that can fit within the rollers and plates of the
chain and engage the power train.
Older one and three speed bikes use the thicker 1/8" chains.
Thinner 3/32" chains are used on derailleur "6 speed
and up" bicycles. Chain tooth size then is directly related
to the internal width of the chain and that dictates the thickness
of gears which in turn is specific to the type of bike.
2. How to Measure The EXTERNAL Bicycle Chain Width?
The external width of a bicycle chain (E-W)
is the maximum width of the chain measuring on the outer edges
of the outer plates or pins, whichever sticks out the most. It
becomes critical the more gears you have in place on the rear
More gears means less space between the individual sprockets
and thus less clearance for the chain. Bicycle sizes thus must
reflect increasing numbers of gears by reducing the overall width
of the chain without affecting the standard 3/32" internal
measurement. Manufacturing innovations like flush mounted rivets
and KMC's bushingless chains have offered solutions in creating
a narrower chain.
Chain manufacturers typically use the number of gears as the
way to differentiate chains for a 10 speed bike versus a thicker
chain for a 9 speed bicycle. You'll commonly see "10s"
or "9s" in the listings rather than referring to the
actual measured external width, although often this information
is available as well.
3. Bicycle Chain Pitch
For a complete conversation about bicycle chain sizes, you also
need to consider the measurement that dictates the distance between
adjoining pins or rivets.
For all purposes, you can consider it a given. All chains produced
today are built with pins machined 1/2" apart. You may want
to read a further discussion on "chain stretch" when
you place a metal ruler against an old chain and find that the
pins don't line up nicely at the 1/2" marks.. a clear sign
that maybe it needs to be replaced.
More to Buying A Chain Than The Width:
Note that although there is a standard bicycle chain tooth size,
both in width and pitch, that is not true in the actual shape
of the gear teeth. Each manufacture designs the tooth shape on
their sprockets slightly differently so finding compatible bicycle
chain-gear-derailleur combinations is an important consideration
before you buy a new chain.
So after all that, to define a bicycle chain size you need:
- Chain Internal Width: 3/32" for derailleur bikes
- Chain External Width: ie. 10s
- Chain Pitch: Typically 1/2"
- Sprocket Shape: Shimano vs SRAM
Bicycle Chains: What's Best to Buy etc.