How do I know what bike chain to buy?
How do I choose? Bike chain selection is firstly decided based upon the “speed” of the chain; this is because it determines the width of the chain. An 11 speed chain for example is narrower than a 9 speed chain, as the sprockets on the 11 speed cassette have a narrower spacing between them.
How do I know my chain size?
To measure the chain size, if you have just the sprocket, use calipers to measure between the teeth. Measure from center to center of where the chain roller would set between the teeth that will give you the pitch. Once you know the pitch you can determine what chain size you would need.