Fly Tying Hook Size Calculator
Find the right hook size and style for any fly pattern.
Covers dry, wet, nymph, and streamer hooks.
Fly hook sizing uses a counterintuitive system: smaller numbers mean larger hooks down to size 1, then it switches to “/0” notation where larger numbers mean larger hooks (1/0, 2/0, etc.). The right hook depends on the fly type, target species, and the natural insect being imitated.
Hook Size Reference — Gap Width (approximate)
| Size | Gap Width (mm) | Typical Use |
|---|---|---|
| 28 | 1.5 | Tiny midges (size 28–26) |
| 24 | 2.0 | Small midges, micro dry flies |
| 20 | 2.5 | Small mayflies (Tricos, BWOs) |
| 18 | 3.0 | Small dry flies, emergers |
| 16 | 3.5 | Standard dry flies (Adams, Elk Hair Caddis) |
| 14 | 4.0 | Medium dry/nymph (Hare’s Ear, Pheasant Tail) |
| 12 | 5.0 | Large dry/nymph (Stimulator, Stonefly) |
| 10 | 6.0 | Large nymphs, small streamers |
| 8 | 7.0 | Streamers, hoppers |
| 6 | 8.5 | Streamers, bass bugs |
| 4 | 10.0 | Large streamers |
| 2 | 12.0 | Large streamers, pike flies |
| 1/0 | 14.0 | Saltwater, big streamers |
| 2/0 | 16.0 | Saltwater, tarpon |
Hook Length Designations
Hooks are also classified by shank length relative to standard:
- 1X short: shank is one size shorter than standard (dry fly hooks)
- Standard: normal length for the size
- 1X long: shank equals the next size up (nymph hooks)
- 2X long: shank equals two sizes up (streamer hooks)
- 4X long: shank equals four sizes up (large streamers, pike)
Matching Naturals to Hook Size
Measure the natural insect body length in millimeters. The hook shank should roughly equal the insect body length.
Hook shank length ≈ Natural insect body length
A size 16 standard hook has a shank of approximately 11 mm, suitable for a mayfly with an 11 mm body.
Worked Example — Blue-Winged Olive (BWO) Emerger
The natural BWO body is about 7–9 mm. A size 18 or 20 hook (shank 8–10 mm) matches well. Use a curved emerger hook (like a Tiemco 2487 or similar) for the natural emerging posture in the surface film.
Wire Gauge
Hooks also vary by wire thickness:
- Fine wire (1X fine): dry flies — lighter means better flotation
- Standard wire: all-purpose
- Heavy wire (1X heavy, 2X heavy): nymphs and wet flies — sinks faster, stronger for big fish
- Stainless steel: saltwater flies — corrosion resistance
Barbed vs. Barbless
Many fly fishers crimp or use barbless hooks for easier release and less fish damage. Barbless hooks require maintaining steady tension during the fight. Some waters legally require barbless hooks.