[FatTireFred]

if you got the cranks, why can't you measure it?

 

[FatTireFred]

Where exactly do I measure from? The outside/middle/inside edge of the bolt? I'm not very accurate with my tape measure...

Well, BCD = Bolt Circle Diameter. For the chainring bolts (the ones that hold the chainring to the crank). Measured center to center. In mm or cm/10. If it has 5 chainring bolts (likely), measure from center of the crank bolt hole (the big one, for the bolt that holds the crank on the bottom bracket spindle) to center of a chainring bolt hole and double it or multiply by 2. You could also verify by measuring from the center of one chainring bolt hole to the center of the next one, and using one of the various conversion tables found on the internet. Simple, huh?