Replacement chains for bicycles are always longer than you need. This video will take you step by step through sizing a bike chain, including determining whether your old chain was correctly sized.
Sizing to an old chain, and the largest cog & chainring method, as well as some exceptions and considerations such as rear suspension and chain guides.Watch the full tutorial on the video from Park Tool:
Before we begin the chain sizing process, let’s first define the two types of multi-speed bicycle chain. There are chains that use a master link and chains that use a special connecting rivet chains. Master link chains use two removable outer plates to connect the chain. Connecting rivet chains use a special rivet to connect the chain.
Too long chain will increase risk of chain dropping, while too short chain puts too much stress on the drivetrain, or can damage it, if it can be put and closed over the chainrings in the first place. Chain that is too short can also damage rear derailleur.