Tippet X-Rating to Pound Test Calculator
Convert tippet X-rating (0X to 8X) to pound test, diameter in mm and inches, and matching fly hook size.
Standard fly fishing reference.
The X system is a leftover from horse hair leaders. When fly fishermen drew gut leaders through plates to thin them, each pass was an “X.” More X means thinner. 0X is the thickest, 8X is fishing-thread thin. The number is also a quick way to call diameter in thousandths of an inch.
The diameter math. Tippet X = 0.011 - (X × 0.001). So:
- 0X = 0.011" = 0.28 mm
- 1X = 0.010" = 0.25 mm
- 2X = 0.009" = 0.23 mm
- 3X = 0.008" = 0.20 mm
- 4X = 0.007" = 0.18 mm
- 5X = 0.006" = 0.15 mm
- 6X = 0.005" = 0.13 mm
- 7X = 0.004" = 0.10 mm
- 8X = 0.003" = 0.08 mm
Pound test does not scale linearly. Modern fluorocarbon and copolymer tippets break around 25 to 30% stronger than old-school nylon at the same diameter. Trout Hunter, Rio Powerflex, and Seaguar all publish slightly different breaking strengths. Use these numbers as guideposts, not gospel.
Matching tippet to fly size. The “rule of 4” is what most guides use: divide the hook size by 4 to find the X. Hook size 16 / 4 = 4X. Hook 12 / 4 = 3X. Hook 22 / 4 = 5.5X (round to 5X or 6X depending on water clarity).
When to break the rule.
- Spooky trout in clear water: go one X thinner than the rule says.
- Big streamers and saltwater: ignore X entirely. Use straight 12 to 30 lb fluoro.
- Czech nymphing: thicker tippet (3X to 4X) so you can horse fish out of fast water.
Fluorocarbon versus nylon at the same X. Fluoro sinks, nylon floats. Fluoro is less visible underwater but slightly stiffer. Fluoro costs 2 to 3x more. For dry fly work, nylon is fine. For nymphs and subsurface, fluoro pays off.
Keep your spools labeled. Once you take the printed sleeve off a tippet spool, you cannot tell 5X from 6X by eye. Sharpie the X on the spool or you will tie a #22 BWO to 4X tippet and wonder why no fish are eating.