According to my research, the American Sportfishing Association in conjunction with the Cortland Line Company helped develop a fly line standard so that manufacturers could create a system for matching the right fly line to the right fly rod. Hence, the weighting system was born. Fly lines range in weight from 1 to 15. A 1-weight fly line is the lightest in terms of weight (grains), while 15 is the heaviest. Typically, fly lines come in lengths of 90 feet. The weight of the line, however, is determined by the first 30 feet of that line. With that in mind, a fly line chart for weights 1 through 10 is at the bottom of this page.
There are also acceptable variations of weight between lines, usually plus or minus six to twelve grains. So a “standard” 5-weight line could weigh 134-146 grains and still be acceptable.
The weight of the fly line is critical in the delivery of the fly to the fish. The weight of the line is what loads the rod while casting, which creates kinetic energy which is then transferred to the spot where you wish the fly to land. Lower weight lines are generally considered “finesse” lines. While delivering size 16 to 28 midges to small stream summer trout, for instance, a 1- or 2-weight would be your best choice. The weight is enough to cast very small flies while also creating the least amount of disturbance once it hits the water. Also, the water in summer is low enough that current doesn’t play a big factor. In other words, you don’t need a line heavy enough to battle both the current and the fish, as you would in the spring when water levels are higher and currents are stronger. If you used a 1-weight line in the spring, you might not land many trout because you don’t have enough torque to actually wear out the fish before it finally throws the hook. For that reason, my go-to setup for spring trout fishing is a 4- or 5-weight line matched to a 4- or 5-weight fly rod.
Keep in mind, too, that it’s not absolutely necessary to match the line weight to the rod weight. One of my favorite setups for steelhead is an 8-weight rod coupled with a 7-weight line. The heavier rod makes it easier to cast the comparatively lighter line, which affords me more distance and control, both of which can be valuable assets when approaching spooky fish. Also, the heavier rod helps offset nasty wind and weather conditions that can affect casting to winter steelhead, while the lighter line delivers a better fly presentation.
With that said, though, I would never pair a rod with a line more than two sizes smaller or one size bigger. Too far outside of the weight range and you lose too much casting control and end up wasting energy trying to get the fly where you want it to go. That’s the whole reasoning behind rod and line weights, after all. If you match the right rod and line weight to the conditions and fish you are pursuing, you’ll find it much easier to cast and control your fly. In that regard, the fly line chart can really come in handy.
Fly lines can also be bought with various tapers. In my experience, straight lines (or level lines) have no value at all because they are difficult to cast and offer very little control. There are numerous sub-categories of lines on the market, but my two favorites for trout and steelhead are weight forward and double taper.
Weight forward line means that most of the weight of the line is found in the front half of the line and it’s great when making 20 to 80-foot casts. These are perhaps the easier lines to cast if you’re new to fly fishing or fish a lot of nymphs and streamers. They can be roll cast easily in tight situations with minimal effort. In a way, I liken fly casting to throwing a spear. Imagine that the spear is front-heavy. It’s easier to get long distance accuracy with a front-heavy spear than with a back-heavy spear.
Double taper line is a good option, too. Whereas weight forward line starts with a smaller diameter and then quickly shifts to a larger diameter before eventually settling back to a small diameter in the back half of the line, double taper starts small and gradually thickens and then gradually tapers to small again. This type of line is ideal for casting dry flies to stream trout. Their ideal casting range is slightly less than weight forward lines, generally topping out at around 50 to 60 feet.
Without a doubt, fly line technology has advanced tremendously the past few decades. We’ve come a long way since horsehair and silk fibers. There are so many brands to choose from today, but if you consider the conditions and the fish you are trying to catch, deciding which size and style to use doesn’t have to be rocket science. •