The starting point is always to consider which type of fly you would need for the water you are fishing. When you know which size of fly you are going to put on the leader, then you will also have an idea of the line weight needed. For example, a large and heavy fly takes a heavier line (which equals a higher line weight) in order to be able to cast and present the fly properly. The following table is a list of different line weights and what I believe are the fly sizes that match those line weights for trout and salmon fishing.
The weight listed below is the loading weight for any of our line systems. The weights listed are the actual weight for a shooting head, or the weight of a belly if it is a weight forward line.
Compared to the Logic nylon leaders, the Logic coated leaders enable you to cast bigger flies and also allow you to have more control over which water column your fly will be fishing. The recommendation below only takes Logic coated leaders into account. However, do not count or include the leader’s actual weight as part of the loading weight – because it is not! If I had to go into more detail here, this recommendation would turn into a long and detailed article, so please just take my word for it.