Originally Posted by well biked

The method barba is talking about is the largest chainring/largest cog method, probably the most common chain sizing method there is. Put the rear derailleur over the smallest cog (to get it out of the way), and the front derailleur over the largest chainring. Put the chain through the front derailleur and over the largest chainring, and also over the largest cog in the rear. Pull the chain tight, look at where the nearest point the chain could join is, add a couple of rivets (an inch), and there's your chain length. If you're going to use a connector link (SRAM Powerlink, etc.), don't forget to account for it-