Fly Line Weight

As every angler knows, fly lines come in different weights. So, an angler might wonder, what is the weight of the fly line referring to? Good question. Here's the answer. All manufacturers weigh their fly lines, and the measure of weight used is grains (there is 14 grains in a gram, in the event you didn't know this well-known fact).

Scientific Anglers Floating Fly Line for Trout
Scientific Anglers Floating Fly Line for Trout. See more Scientific Anglers Trout Line at FishWest.

Happily, recognizing that America has no love affair with the metric system, fly line manufacturers have adopted an easy to remember "scale" to help anglers quickly determine fly line weight. This scale runs from 1-14 (and, it should be noted, is occasionally added to). The smaller the number, the lighter the fly line is. And conversely, the bigger the number, the heavier the fly line will be.

So, why is this important? It's quite simple. You see, the weight of the fly line determines what you fish for. In other words, get the wrong fly line weight and you can watch your probability of successful fishing slip away faster than snow under the Arizona sun.

Thus, before continuing, it is helpful to know which fly line weight is best used for particular types of fishing.

Fly Line Weight Determines What You Fish For

Yep. The title says it all. Before buying that fly line from a nice online store or your friendly fly shop, you need to know what you plan on fishing for first. The guide below will help you do just that:

  • Fly Line Weight 1-3 : This weight is primarily for small fish - panfish, very small trout or, in somewhat rare circumstances, larger trout very tiny streams.
  • Fly Line Weight 4 : This weight works just fine for panfish, too. But also works well for all but the largest of trout. Best used on small/mid-sized streams and where longer casts aren't needed.
  • Fly Line Weight 5 : The "all-around" trout fisherman's line weight. Covers virtually all trout-fishing situations an angler is likely to find. Works ok for smaller fish too, but not as fun to catch small fish on as a fly rod outfit that has a lighter fly line. This weight also works ok for smaller bass fishing, particular smallies in rivers.
  • Fly Line Weight 6 : Another good "all-around" weight for trout fishing. Overkill for tiny trout and panfish since the stouter rigs needed for heavier fly line kills the fun out of catching small fish. But ideal for large trout and all but the largest bass, too.
  • Fly Line Weight 7 : At least here in Montana, you won't want to use this line for trout fishing in a river. Instead, Weight 7 fly lines are best used for larger, more powerful fish such as bass, smaller salmon, and steelhead.
  • Fly Line Weight 8+ : The fly line weights from 8 upward are designed for very powerful, very large fish, saltwater and salmon species in particular. If you fish freshwater, you won't have much call for this line weight unless chasing the large salmon found in Alaska.

How Does Fly Line Weight Relate to the Fish I Chase?

Good question, but one that is also easy to answer. On the previous page it was mentioned that the fly line itself is responsible for casting the fly. What this means is that the fly line weight needs to match up with the size of the flies you plan on using when fishing. And the only way to really know what size flies you plan on using is if you know what you plan on fishing for.

For example, trout flies generally fall in-between the range of size 0 to size 22, with the most commonly used hook sizes being 10-16. These are small hooks and the flies are usually feather light. If you use too heavy of a fly line with these lightweight flies, what happens is that the fly slams into the water propelled by the heavy weight of the fly line. This is, needless to say, not especially desireable when fishing for trout. Moreover, not only will the fly likely slam into the water, it probably will not be properly presented, either (landing upside down or on its side).

Conversely, lets' say you are chasing large, wary brown trout with streamers. Hooks on large streamers are sizable and the weight of the fly itself is often substantial. If you fish a big streamer on too light of a fly line, you'll have poor control over the fly and the cast. While you'll still be able to "make the cast," the cast is highly likely to go anywhere but where you want it to go. And, just like before, all presentation of the fly is likely lost as well.

Remember, when you use too light of fly line weight for a heavy fly, you are also using a light fly rod and a light fly reel (a fly rod outfit consists of a fly rod, fly reel and fly line that all match, exactly, in weight).

Because of this, not only is the fly line not heavy enough to properly toss the fly, the fly rod itself is not powerful enough to power the fly line, either. An angler thus has two strikes against them before making a cast, which isn't exactly conducive to productive fishing.

A Quick Suggestion for New Anglers

For trout fishing, new anglers should focus on line weights 4-6. I personally prefer a four weight fly line (and matching fly reel and fly rod). The reason is because a lighter fly fishing outfit makes smaller fish more fun to catch. I also tend to prefer fishing smaller to mid-sized rivers, and rarely find myself wanting to make 30 yard casts.

Moreover, a lighter fly line weight works very well for lazy days when chasing panfish, whitefish or small to mid-sized bass.

In other words, I find a four-weight fly line works best for me. Whether or not it will work best for you is dependent on the types of fish you plan on chasing and whether or not you need to make long casts (heavier fly lines will cast further when paired with a equal weight fly rod, in general).

But if you don't foresee yourself chasing trophy trout, large bass, salmon or needing to make real long casts, a 4-weight or 5-weight fly line really should be all a new angler needs to start with.

Well, that covers fly line weight. But we aren't even close to being done. You see, figuring out what fly line weight to use, and why. is just the first step in determining the type of fly line to use.

The next step is Understanding Fly Line Taper and how it relates to fly fishing, particularly casting.