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What Size Fly is Best for Trout?

The best size fly for trout depends on the fish size and location. A size 18 is about average. You can try larger and smaller, experimenting is part of the fun of fishing.


If you know already what’s the best line weight, hook, or color line for fishing trout, there’s still one small detail that you should consider, before going to that place you know is filled with fish: size fly. As fishing equipment is diverse, it can be confusing or even challenging to choose the most suitable piece. But size fly could be easy to choose if you pay attention to the right things. Which things?

  1. Trout size

Trout differ in size, type, and places they live in. You have to take account of these things when choosing the right size fly. Trout can weight from 1.5 lbs. up to 20 or more. So, you can imagine that there are many differences between them, from their appetite to the size fly.


  1. Types of flies

Now, with such a variety of flies to choose from, you might have difficulties in differentiating between them. But simply put, they can be divided into 3 categories.

The first 2 categories are flies that float, and flies that don’t. What you need to know about each of them, however, is their purpose. With those that float, it’s obvious that they resemble insects that sit on top of the water, inviting the prey to get them. On the contrary, those that don’t float are available for trout whenever, as they are underwater.

The 3rd category consists of naturals that don’t resemble insects, such as minnows, or baitfish patterns. They don’t float, but they resemble the organisms that can be found in trout’s environment and with which they are accustomed to.


  • Flies that float

The dry flies are made of either fur or feathers or anyway, of natural materials. They sit on top of the water and wait for trout to come for them. Experienced anglers warn about these flies: the moment trout gets at them, in their initial state of floating, they will sink and trout won’t eat them anymore. So it’s recommended to use a silicon-based flotant beforehand. Simply apply it to the feather section of the fly, and the fly will last longer when floating.

Also, a trick recommended by fishermen about the dry flies: if you’ve used them to catch multiple fish and they seem to have absorbed too much water, apply a desiccant. Simply put, take the dry fly, put it in the desiccant also known as easy dry, and shake that bottle. The fly will dry and will be good to float again.


  • Flies that don’t float

The anglers that use these types want the flies to get underwater as fast as possible. But that doesn’t always happen according to the plan, even if these flies are designed for that, so it’s recommended to use a split shot above the fly for faster sinking.

  • Size fly

You should know that when it comes to the size fly, the bigger the number, the smaller the fly. Usually, the dry flies range from size 16 to 12, but most choose 20 to 22. Size 6 to 4 is useful regarding streamers. Although plausible to believe that for bigger trout you need bigger flies, it’s not a rule of thumb. Experienced anglers, with a highlight on experienced, use smaller size fly to catch trout. Some use size 22 flies to catch big trout, so it’s really no rule. It’s experience and skill.

Now, you should consider other details as well, such as the place you’re going to and the flora and fauna there, the type of fish, the time of the year, the rest of your equipment, and so on.

Also, fishing stores are not just a realm of the unknown for beginners, you can find some help from people there.

As an idea, trout size flies can be found from the size 0 to 22, applying the same concept of the bigger, the smaller. Take account of what hooks you use, as those differ in size as well, and the fact that generally, for trout you should opt for size flies 10 to 16.


With one of the biggest mysteries in terms of fishing trout solved, you are ready to catch that fish with the best size fly.

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