Fly Fishing Tippet Size Calculator
Match tippet X-size to fly hook size and breaking strength.
The rule of 3 and rule of 4 explained.
Essential for fly fishing leader selection.
In fly fishing, the tippet is the fine end of the leader that connects to the fly. Tippet sizes use an X-rating, and a higher X number means thinner and weaker.
X-rating to diameter: Diameter (inches) = (11 - X) × 0.001
| X | Diameter | Nylon | Fluorocarbon |
|---|---|---|---|
| 0X | 0.011" (0.28 mm) | 15.5 lb | 20 lb |
| 1X | 0.010" (0.25 mm) | 13.5 lb | 17 lb |
| 2X | 0.009" (0.23 mm) | 11.5 lb | 14 lb |
| 3X | 0.008" (0.20 mm) | 8.5 lb | 11 lb |
| 4X | 0.007" (0.18 mm) | 6 lb | 7.5 lb |
| 5X | 0.006" (0.15 mm) | 5 lb | 6 lb |
| 6X | 0.005" (0.13 mm) | 3.5 lb | 4.5 lb |
| 7X | 0.004" (0.10 mm) | 2.5 lb | 3.2 lb |
| 8X | 0.003" (0.08 mm) | 1.75 lb | 2.2 lb |
Those are the same figures the tippet X-rating calculator uses, so the two pages agree. Diameter is a standard. Breaking strength is not: Rio, Trout Hunter and Seaguar all publish slightly different numbers for the same X, and modern copolymers run 25 to 30% stronger than the nylon these figures are based on. Treat them as guideposts.
Rule of 4: Divide the fly hook size by 4 to get the X-rating. Hook 16 gives 4X, hook 12 gives 3X. This is what most guides quote, and it is the safer default because it errs toward tippet that turns the fly over and lands fish.
Rule of 3: Divide by 3 instead for a finer, more forgiving drift. A size 12 fly comes out at 4X rather than 3X, one step thinner. Use it for dry flies, flat water and fish that have seen a lot of anglers.
The two rules disagree by roughly one X across the whole range, which is about as much as the difference between two brands anyway. Neither is wrong.
When to override both:
- Spooky fish in clear water: go one X finer than the rule says
- Big streamers and saltwater: forget X entirely and use straight 12 to 30 lb fluorocarbon
- Czech nymphing in fast water: go heavier, so you can horse a fish out before it reaches the next boulder
Fluorocarbon sinks and is harder to see underwater, which suits nymphs. Nylon floats and is more supple, which suits dry flies, and it costs a third of what fluorocarbon does. One practical note that has nothing to do with the math: once the printed sleeve comes off a spool you cannot tell 5X from 6X by eye. Write the X on the spool in marker, or you will tie a size 22 midge to 4X and spend an hour wondering why nothing eats it.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.