Motorcycle chains and sprockets are matched for proper fit, both by length and width. A chain of the proper pitch, but a wider width, will fit a narrower sprocket. However, in high-performance applications this is not recommended, as improper chain adjustment can result in the bending and premature wear of socket teeth. Modern o-ring chains and lightweight sprockets can be extremely expensive, so proper care and fitment is a must.
Measure the distance from centre of roller to centre of roller on the chain. The chain size is based on eighths. The first number of the chain size is the distance between roller centres, in eighths of an inch. A 420 chain will be 4/8 or 1/2 inch from roller centre to roller centre.
Measure roller width, giving you the second number in the chain size. Chain roller width is the last two numbers in chain size separated by a decimal. the 420 chain has a roller width of 2.0/8, or 1/4 inch.
Put the two numbers together to give you the overall chain size. If your first measurement between roller centres was 5/8, and your second measurement was 3/8, you have a 530 chain. If you have a Suzuki chain, it may measure slightly more than 3/8 in width. This is an odd chain size known as a 532. However, it will run well on a 525 or 530 sprocket of any make.
When replacing a worn chain, replace sprockets as well. Never mix new and old parts. Remember that a wider chain will run on narrower sprockets, but usually a narrow chain will not fit and run smoothly on wider sprockets.