How Fly Hook Sizes Work
Fly hook sizes use a reverse numbering system: the larger the number, the smaller the hook. A size 20 hook is much smaller than a size 12, and a size 12 is smaller than a size 8. Standard sizes are usually even numbers.
Which Hook Is Bigger?
Quick answers to common questions:
- #2 or #4: A size 2 is bigger than a size 4.
- 12 or 14: A size 12 is bigger than a size 14.
- #1 or #8: A size 1 is bigger than a size 8.
Think of the number as “how many steps down from a big hook” and it becomes easier to remember.
Hooks Larger Than Size 1: Aught Sizes
After size 1, the numbering switches to “aught” sizes written like 1/0, 2/0, and 3/0, and spoken as “one aught” or “two aught.” In this range the pattern flips: the larger the number, the larger the hook. A 2/0 is bigger than a 1/0. These are common for saltwater flies (see saltwater fly fishing techniques) and big predator flies such as pike and musky streamers (see northern pike fishing).
Simple Hook Size Chart
These ranges are approximate and vary by source, pattern, and region. Treat them as starting points rather than strict rules.
| Fly type | Common sizes | Notes |
|---|---|---|
| Small dry flies (midges, small mayflies) | 18 to 24 | Light-wire hooks help flotation |
| Medium dry flies (mayflies, caddis) | 12 to 16 | Common all-around range |
| Large dry flies and attractors | 8 to 10 | Hoppers and big stoneflies may run larger |
| Small nymphs and emergers | 16 to 22 | Often fished in clear, low water |
| Standard nymphs | 10 to 14 | Mayfly, stonefly, and caddis nymphs |
| Larger nymphs and wet flies | 6 to 8 | Heavier wire helps them sink |
| Trout and bass streamers | 4 to 10 | Longer shank hooks are common |
| Large streamers | 2 to 6 | Strong wire is helpful |
| Saltwater and predator flies | 1/0 to 6/0 | Strong, corrosion-resistant hooks matter |
Hook Size by Target Species
- Trout: Roughly 10 to 24 for dry flies, nymphs, and emergers, and 4 to 8 for streamers (see must-have trout flies).
- Panfish: Often small, around 8 to 12 for poppers and spiders.
- Bass: Often about 2 to 10 for poppers, streamers, and crayfish patterns.
- Pike and musky: Commonly 3/0 and larger for oversized flies.
Beyond Size: Hook Anatomy
The number is only part of the story. Key parts include:
- Gap: The distance between the point and the shank. A wider gap can help with hooking, but hooks of the same number from different manufacturers can differ in actual size.
- Shank: The straight part behind the eye. Hooks may be standard, 1X long, 2X long, or longer, and short-shank versions exist as well.
- Wire weight: Fine wire for dries, standard or heavy wire for nymphs and streamers. A designation like 2X heavy means thicker wire than standard.
- Barb: A barbless hook or a pinched barb is easier to remove and is required on some waters. Check local regulations.
- Point and bend: Different shapes suit different flies, such as curved nymph hooks or straight-eye dry hooks.
How to Choose a Hook Size
- Match the size of the natural insect or baitfish where possible.
- Choose a hook weight that matches the fly’s job: floating or sinking.
- Consider the fish. A small hook can hold small fish well but might not be right for strong or large fish.
- Pair the hook with an appropriate tippet (see fluorocarbon vs mono line) so the fly can move naturally. A common rule of thumb pairs thinner tippets with smaller flies, but charts differ.
If you are unsure what size a fly in your box is, see our guide on identifying fly fishing flies. New to gear in general? Our beginner guide to starting fly fishing covers what to buy first, and the fly fishing terms glossary explains terms like gap, shank, and aught.
A Note on Measuring
Because manufacturers differ, a size 14 from one brand may look slightly different from another. Compare hooks side by side with a ruler or a printed chart from the maker if exact sizing matters.