Ideally, determining the length of your new chain is as easy as measuring your old one. But what if you’re not sure your current chain has the correct length?

Before we start, let’s determine what kind of chain connector you (new) chain has. There are two forms of multi-speed bicycle chain connectors: master links and rivets. Master link chains are linked by two removable outer plates. These can be removed without special tools, although a missing link plier may come in handy. A special rivet is used to bind connecting rivet links, and you’ll need a special rivet tool to remove and place these. Check out our article on replacing your bike chain for detailed instructions on replacing your chain.

Determining the length of your bike chain

Method 1

Comparing chains.

Place the old chain next to the new chain. Outer plates should always be lined up with outer plates, and inner plates should always be lined up with inner plates. If an end with outer plates is being compared to an end with inner plates, make sure to account for that difference. Match them rivet by rivet, keeping in mind that old chains will lengthen over time.

Method 2

SiIng to the largest cog and largest chainring

To begin, change the front derailleur to the largest chainring and the back derailleur to the smallest cog. Wrap the chain around the largest rear cog first. The new chain should be routed toward the front chainring. Pass the chain end through the front derailleur cage and onto the largest front chainring. Now bring both ends together, without going through the rear derailleur cogs. The correct chain length is where the two ends meet, plus two chain links.  

Parktool has a great video about this.