How tippet sizes work
Tippet is the thin, clear line between the end of your leader and the fly. Its size is given on an X scale that measures diameter: the larger the X number, the thinner the line. 0X is 0.011 inches, and each step up takes off a thousandth of an inch, so 5X is 0.006 inches and 8X is 0.003. Subtract the X number from 11 and you have the diameter in thousandths.
Match the tippet to the fly
Orvis's rule of thumb is to divide the hook size by 3 and round. A thin tippet lets a small fly drift naturally; a thick one stiffens it and can stop a big fly from turning over. Heavier flies, bigger fish, fast water and snags all call for going a size heavier. Flat, clear water and wary fish call for going lighter.
Pound test is not the X size
Because the X scale only fixes the diameter, two spools of 5X can have different breaking strengths. The strengths in this chart are Orvis's figures for its Super Strong nylon. Fluorocarbon and newer nylons often test higher at the same diameter, so check the label on your spool when strength matters.
Continue the leader's taper
Add tippet one size finer than the end of your leader, for example 4X on a 3X leader, then tie the fly to the tippet. Adding tippet this way also saves your leader from getting shorter every time you change flies.
Choosing the rod and line first? The fly line weight chart gives the line weight and rod length for each fish.
The chart as an image
Save it to your phone or print it for the inside of a fly box lid.
