The size and weight of the fly determines what size tippet works best with that fly. A 3wt rod is for smaller flies and the leader will have a lighter tippet. If you were fishing a size 16 fly a 5X tippet would be used. If you were fishing an 8wt rod with a size 6 fly, a size 2X tippet would be called for. The companies making the leaders size the butt of the leader to match a group of fly lines it might be used on. All you have to worry about is what size tippet you will be using for a particular sized fly.

Tippet Diameter | Tippet Size | Pound Test | Fly Size |
---|

.003 | 8x | 1.2 | 24-26-28 |

.004 | 7x | 2 | 20-22-24-26 |

.005 | 6x | 3 | 16-18-20-22 |

.006 | 5x | 4 | 14-16-18 |

.007 | 4x | 5 | 12-14-16 |

.008 | 3x | 6 | 10-12-14 |

.009 | 2x | 7 | 6-8-10 |

.010 | 1x | 8.5 | 2-4-6 |

.011 | 0x | 10 | 1/0-2-4 |

.012 | x1 | 12 | 2/0-1/0-2 |

.013 | x2 | 14 | 3/0-2/0-1/0-2 |

.014 | x3 | 16 | 5/0-4/0-3/0-2/0 |

.015 | x4 | 18 | 6/0-5/0-4/0-3/0 |

NOTE: Leader diameters and strengths vary from manufacture to manufacture and with different materials or processes.

Here is a quick way to calculate the best size tippet to use on the water. You take the fly size and divide it by 4 and then add 1. For example, take a size 6 hook, divide 6 by 4 and you get one. Add one to that and you get 2. So for a size 6 hook use a 2X leader. You will note that the chart says 1X or 2X will work. The formula is a guide to get you close to the proper sized tippet on the water. In this case you use the leader that is most appropriate for the size of the fish.