The Global FlyFisher
Simply the Best Place to go for Online Fly Fishing and Fly Tyinghttp://globalflyfisher.com/fish-better/leader-formulas
In order to calculate the proper formula of a fly fishing leader, you need to understand the basics of leader design.
Components of a Leader
There are three main components of a leader: Butt, Taper (also called mid-section or graduation), and Tippet. The most common formula basis for the leader is 60% butt, 20% taper, 20% tippet. Other formulas such as double taper formulas offer 40%,20%,40%, but for the most part, formulas are
derivatives of the 60/20/20 rule.
According to Charles Ritz in his book "A Fly Fisher's Life", the diameter of leader butts should be 60% of the diameter of the end of the fly line. Other formulas indicate that 75% is the optimum butt diameter, but in either case, a leader butt of .017" to .022" satisfies most any formula. A leader butt of 60%-75% is quite ample enough to transmit and disperse casting energy downward to the tippet. Also consider the stiffness of the butt material. It should approximate the stiffness of the fly line. Use the Table 1 to guide you in selecting the correct leader butt thickness.
Again, Ritz reminds us that the ideal is to have the longest forward taper as possible while still remaining under control during the presentation. He subscribes to the 60/20/20 rule, where the 60% is strength, 20% is taper and the final 20% is terminal tippet.
According to Ritz, suppleness in leader material is only necessary at the tippet, where, in his opinion, 20 inches is the ideal length.
Other sub-parts of a leader are: Shock Butt, Shock Tippets and Wire Tippets. These components are geared toward specialty fishing situations like toothy fresh and saltwater critters. This document will not go into great detail in these areas.
Recommended Fly Sizes for Tippets