General Chain Length Information:
All motorcycle chain lengths are expressed by the number of pitches or rollers within it. So if you have an old chain that is in need of replacement and you wish to check the length - just count the number of rollers in it including the rollers on each end. If the number is an odd number, then it must have a half link in it. If the chain is very worn, and its history is unknown eg. you have purchased a motorcycle with a worn chain on it, please be aware that sometimes a roller or two may have been removed by the previous owner in an attempt to re-adjust it. In such cases, there is a danger of purchasing a new chain which is too short - so if there is any doubt - it is always better to purchase a new chain which has more rollers than the worn one.
To calculate approximately how many rollers are needed - if you can take a measurement in inches for example by using some string then divide the number of inches by the pitch for the relevant chain size eg. 65 inches divided by 0.625 (the pitch for 5/8") = 104 rollers.