Beginner's Corner: The Right Size Line

To a novice fly angler, the fly line size system used in fly fishing is often a confusing jumble of numbers. What fly line size do I need for trout? Can I fly fish for any other kinds of fish with my trout rod? What size flies can I use on my rod? Because the fly line size is the first thing you should decide when picking a fly fishing rod, and it will determine what you can do with the rod, it's a pivotal decision.
Fish Species
Trout with small flies, small streams                                        
Trout in small to medium-sized rivers                                        
Trout in big rivers and lakes                                        
Freshwater bass and pike                                        
Atlantic salmon                                        
Pacific salmon                                        
Sharks and barracuda                                        
Striped bass, bluefish, false albacore                                        
Tunas, sailfish, marlin                                        
Fly Sizes 6/0 5/0 4/0 3/0 2/0 1/0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
Fly Line Weight                                        

To use this fly line chart to find the most common fly line size used for the species you'll be pursuing, draw a line straight down from the middle of the size range for your species (green bar) to where it intersects the middle of the fly line size ranges (yellow bar). This will not only give you the best all-around fly rod for that species, it will also give you an idea of what other kinds of fish you can chase with the same fly rod.

For example, if you draw a line down from the center of the fly size range for freshwater bass and pike, you'll see that you could also use the same fly rod for steelhead, Atlantic salmon, striped bass, bonefish, and also permit and tarpon with smaller-size flies.

Unless you'll be fly fishing for trout in large rivers or lakes, you'll see that you might be fishing fly sizes in anything from a size 4 through a size 20. Looking down, you'll see that fly line sizes could be anything from a 1-weight to a 9-weight.

  • Unless you will only be fishing big size 4 streamers all the time, you can rule out fly line sizes 8 and 9.
  • Unless you'll only be fishing tiny flies, you can forget about the 1, 2, and 3 fly line weights.
  • When most of your flies will be on the smaller size, stick with the smaller fly line size 4.
  • If the majority of your flies will be larger, or you'll encounter a lot of wind, use the heavier 6 or 7 weight.
  • And, of course, if you want to cover all your bases choose the 5--which is the most popular trout line size by a large margin!

Baffled by the jargon used in fly fishing?
You may want to visit our illustrated Fly Fishing Beginner's Glossary.