20 pitches
 

I understand the service limit for a chain is up to 12.6 inches (319.4mm) for 21 pins.

Might anyone know what the beginning figure is? Meaning, on a brand new chain, what is the length of this distance?

I am curious as to how much my chain has already stretched...

Thanks.

Well it's a 5/8" pitch chain, so 5/8 x 20 = 12.5".

This tallys, generally, with the rule of thumb that says that a chain is duffed when stretched by 2-3%

Thanks Sid.