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Why are Fly Lines Getting Heavier?

The majority of fly lines on the market today no longer conform to industry line weight standards.

Why are Fly Lines Getting Heavier?

The fly line standards we use today are based on the weight of the front 30’ of fly line because that was considered an average cast for trout fishing in 1960. Today, flies are larger, the species we catch are more diverse, and the distances we cast are far greater. (Brian Grossenbacher photo)

This article was originally titled "Weighty Matters" in the April-May 2018 issue of Fly Fisherman magazine.

Many fly fishers don’t realize that the majority of fly lines on the market today no longer conform to industry line weight standards. Check the front 30' of ten different 6-weights, and you may find them running from 160 grains (the standard) up to 235; that’s actually a 9-weight according to the standard. I found 8- and 9-weight lines that tipped the scales as 11-weights. Many fly fishers are shocked to learn that some 5-weight lines are heavier than standard 7-weights.

If you’re a beginner, you should still probably buy a 5-weight line to go with your first 5-weight rod—it’s a reasonable starting point. But if you want to become a proficient fly fisher, you should understand how variable line weights can actually be, and how that affects your results. If you don’t understand the differences, it can lead to poorly balanced tackle, and render tackle discussions or recommendations useless because you’re not making apples-to-apples comparisons. Once you comprehend these not-so-subtle differences between fly lines, it will help you make better purchasing decisions, and put you in a position to use the best fly line for the job.

Misinformed about Fly Lines

I followed one discussion thread on the Internet in which two anglers disagreed about whether a certain rod worked better with an 8- or a 9-weight line. Many others chimed in, about half claiming an 8-weight line was best for that particular rod, the other half arguing the merits of a 9-weight line. However, such debates are meaningless, even ridiculous, until the exact line brand and the specific casting distances are considered.

For example, one angler may cast 30' of a particular 8-weight line that weighs 210 grains and say it’s light, while another angler picks up 35' or more of the same line, which might tip the scale at 260 grains, and argue that line is fine for that rod. Yet a third angler, using a different 8-weight line, one that registers a hefty 310 grains, will have a completely different opinion. While all three fly fishers are debating the merits of an 8-weight line, they are talking apples and oranges. And even that doesn’t account for the flies they are casting, let alone the skill levels of the casters.

How Fly Lines Got Heavier

Fly fishers have become slaves to the numbers without understanding the variables. Up until the 1950s, most lines were silk, and their densities fairly consistent. Lines were identified alphabetically with the letters denoting diameters, for example A (.060"), C (.050"), D (.045"), etc. Thus, a double-taper HDH tapered from a D (.045") down to a fine H point (.025") at each end. The system worked fairly well, because most fishing involved shorter casts for trout with smaller flies.

But the sport changed, followed by a series of developments in tackle. With the popularity of competitive distance casting in the 1940s and 1950s, three-diameter lines were developed. GAF designated a weight-forward, swelling from a G (.030") front end into a thick A belly (.060"), then tapering off to an F (.035") running line. Eventually, as lighter polyvinyl chloride (PVC) lines entered the market, larger-diameter lines were needed to achieve the same load. The standards were no longer accurate.

Line weight, not diameter, loads rods, so in 1961 the American Fishing Tackle Manufacturers Association (AFTMA) created and adopted the familiar line weight standards we have used for nearly 60 years. (AFTMA no longer exists, but the same line weight standards have been adopted by today’s American Fly Fishing Trade Association, or AFFTA.)

The AFFTA standard measures the grain weight of the first 30' of the fly line. (There are about 437 grains in an ounce, so an 8-weight line comes in at close to a half ounce.) Weighing the first 30' of line worked fairly well for trout fishers in the 1960s and 1970s because a 5-weight line transports a #10 Mickey Finn or a #18 Adams with about the same effort, and most trout fishing takes place within the 20' to 40' range.

But changes kept coming. Extremely dense sinking lines were developed. Saltwater fly fishing as we know it today was in its infancy when the standard was first introduced. Exotic species like roosterfish, peacock bass, and dorado were largely unheard of. Fly fishers today travel more, catch a wider range of gamefish, and in part due to the influence of tournament casting, catch fish at greater distances than we did in 1961.

As a result of the growth of our sport, the terminal 30' on which the entire standardized system is based no longer applies for many types of fly fishing. Let’s face it, if you’re fishing for striped bass, you don’t expect to limit your casts to 30' with a 10-weight rod. You expect to reach out to 60', 70', or 80', and the longer you cast, the more weight you are casting.

As a rule of thumb, the weight of the fly line outside the rod tip goes up or down about one line size for every 5' of line you add or subtract from the 30' standard. So, if 30' of 8-weight weighs about 210 grains (the AFFTA standard), 35' of 7-weight weighs approximately the same, as does 40' of 6-weight, or 25' of 9-weight. Conversely, 40' of 8-weight can be the equivalent of a 10-weight. Amazingly, many fly fishers aren’t aware of this simple fact.


Rod manufacturers, wisely anticipating the fact that many fly fishers load their rods with much more weight as they extend line well beyond 30', have been systematically beefing up their rods to accommodate real-life fishing situations.

After all, no one makes a tarpon rod for peak performance at 30'.

Why are Fly Lines Getting Heavier?
Fly rods today normally have just one line size printed on them, when in fact they can cast a wide range of line weights in varying circumstances. (Christiaan Pretorius photo)

At the same time, line designers, in an effort to help casters load those powerful, new, space-age rods, have developed lines for different purposes, by concentrating additional weight up front in their lines, particularly for casting larger and heavier flies, or creating lines with longer heads for greater distance. In so doing, they have eclipsed traditional line weight standards.

Both types of manufacturers are making sincere efforts to help anglers better equip themselves for their sport outside the archaic 30' bubble. As fly fishing continues to expand and change, we may have to change or modify this line weight system, and fly fishers again will have to adjust their thinking, just as they did when switching from letter to number designations more than a half century ago.

Until then, fly fishers should understand that every fly rod handles a wide range of line sizes, certainly much wider than what may be indicated on the rod itself.

Here’s a lesson from outside of fly fishing: Every conventional rod—spinning, casting, surf—has a designated weight range, which overlaps with lighter or heavier rods. I checked out four spinning rods, from “light” to “medium heavy” actions, with suggested lure weight ranges of 1⁄8 to 1/2 ounce, 1/4 to 3/4 ounce, 3⁄8 to 1 ounce, and 1/2 to 11/4 ounce. A 1/2-ounce lure is included within the range of all these rods.

Compare that to narrow windows of standard fly line designations, which never overlap: a 5-weight is 134 to 146 grains; a 6-weight is 154 to 166 grains; and a 7-weight is 177 to 193 grains. The reality is that a 5-weight rod casts lines from 100 to 200 grains, an 8-weight, from perhaps 180 to 300 grains, and a 10-weight easily casts a 400-grain head. Claiming that a rod should cast only a 6-weight line of 160 grains, without qualification, leads too many fly fishers to believe that they must use a line so marked and in fact, many believe that is what they are casting simply because they bought a line with a 6-weight label.

Why are Fly Lines Getting Heavier?
Modern carbon fiber materials and designs help create rods that are lighter and stiffer. To properly load these rods in real-life fishing situations, most fly lines do not adhere to AFFTA standards. Consumers should know the grain weight of the product they are buying, and experiment with the line and rod at actual fishing distances to determine the optimum rod and line combination.

Of course, each time you lengthen or shorten the line, you change the weight of the line you are casting, often going well above or below the specified weight. If you cast 15' of 6-weight line, you may be casting the grain-weight equivalent of a 2-weight. At 30' the line may or may not be a true 6-weight. Extend to 45' and you’re casting the equivalent of a 9-weight. So, in the course of a single day, you are relying on your rod to cast a wide range of weights.

On top of that, there may be 100 different 6-weight lines on the market, and they vary widely in the weight of the first 30', as well as in the weight of their full heads, which can be 30', 40', even 50' long.

Using Lighter Fly Rods with Heavier Fly Lines

An experienced fly fisher once approached me, and asked what line I would recommend for his 7', 4-weight bamboo dream rod. He told me his normal casting distance would be 20', so of course I recommended that he use a 5-weight line of some sort. He was baffled.

He had put a down payment on a 4-weight rod because he wanted to use a light line weight on small streams, but what he should have done is built a 3-weight rod and used a 4-weight line. A slightly heavier line would make it much easier to load the rod at those distances. Here was an angler prepared to lay out $1,200 for a poorly matched outfit.

Similarly, at a recent casting clinic, one student had a stiff, fast-action, 5-weight rod. He had matched it with a 4-weight line because he “wanted to make delicate presentations on limestone streams.” He too was making short casts, with a very long leader, and complained he was unable to unroll the line and leader.

It was obvious that he simply was unable to load the rod adequately. His thinking was the opposite of what it should have been. Either he needed a heavier line, like a 6 or 7, to help him load the rod for his short casts or, since his first priority was fishing a lighter line, to put that 4-weight line on a 3-weight rod.

Understanding Fly Line Weights to Overcome Casting Obstacles

Due to a baggage mix-up, I recently found myself fishing the Texas Gulf Coast armed with a 12-weight rod, but no line heavier than a 10-weight. Huge jack crevalle periodically surfaced close to the boat, and it was difficult to load the rod with a short length of line—especially while using a large, wind-resistant Crease Fly.

My tackle was badly mismatched, so to overcome my handicap, I stripped out extra line and made a 45' cast, which in effect, produced a 12-weight. I pitched the big fly well beyond the fish and hastily stripped back 20' to where the fish actually were. It was not an ideal scenario, but my understanding about line weights allowed me to make some casts and land several fish over 30 pounds.

I’m not at all recommending this strategy, but I am encouraging all anglers to learn more about their tackle so they can make the best of any situation. And if we raise the level of our discussions, we can learn more from each other and from manufacturers. Education is the first step. To recap the points I’ve tried to make: 30' is no longer an adequate measuring stick for many fly-fishing scenarios, so the line weight printed on the box is often erroneous or irrelevant. Consider it merely a starting point in your investigations.

The length of line you are casting greatly affects the loading of the rod; every rod casts a wider range of weights than most fly fishers believe; and for any one numerical line size, there are a multitude of lines made for different purposes, with different designs and weights.

It’s a complex “system” if you can call it that at all, and there are no simple answers. As always, the next time someone asks “what’s the best line for my new X-weight rod,” I’ll have the same response: “It depends.”

A few examples: 

Scientific Anglers Amplitude Anadro fly line

Why are Fly Lines Getting Heavier?

The Anadro is for big fish like steelhead, Atlantic salmon, Chinooks, and cohos in big rivers where long casts and long days slowly stack the odds in your favor. In the 8-weight version, the line has a 62' head with a short, powerful front taper for turning over big flies, and a 30' rear taper for long casts and line control at long distance so you can mend, mend, and mend again. The Anadro taper is available in Scientific Anglers’ Mastery series ($80)—which is smooth—or in the Amplitude series, which has a Sharkskin texture on the tip, a shooting texture through the head of the line, a smooth “tactile reference point” to let you know when the head is extended, and more shooting texture on the running line. Amplitude lines also have a new slickness additive called AST to help the lines shoot farther and last longer than regular Mastery lines. The Anadro taper is 1.5 times heavier than the AFFTA standard. That means the 8-weight is 260 grains in the first 30', halfway between a 9-weight and a 10-weight., $130.

Cortland Tropic Compact fly line

Why are Fly Lines Getting Heavier?

A 350-grain line is an 111/2-weight according to the ­AFFTA standard, but Cortland does a good job here by labeling the Tropic according to its grain weight, and offering multiple suggested rod weights as well. The reality is that this an excellent line for modern 10-weight rods and actual fishing conditions, and the Tropic Compact comes in 200-, 240-, 275-, and 425-grain weights as well. The full-floating line with a short, aggressive head is perfect for casting large-profile baitfish imitations into the wind, or turning over heavy permit flies with dumbbell eyes., $80.

RIO DirectCore Flats Pro fly line

Why are Fly Lines Getting Heavier?

We tested the new RIO DirectCore Flats Pro on Belize permit, alligator gar in Louisiana, and tarpon in the Florida Keys in extremely hot conditions. The low-stretch monofilament core of this new line has zero memory coming off the reel, rolls out straight on the water without kinks or coils, yet it stays stiff enough to shoot long casts and doesn’t tie knots around itself on the casting platform. RIO says the difference is the low-stretch monofilament core that also gives you better contact with the fly, and greater power to bury the hook when you need to. Beyond the new core, the triple-color line helps you judge distances better and communicate more accurately with your guide. The front 19' is blue, while the rear of the body and the rear taper (also 19') is bright orange, followed by 12' of yellow handling line, so it’s easy to both see and feel when you’ve got about 40' of line out of the rod tip. DirectCore Flats Pro 6- to 12-weight lines are all one line size heavy for longer casts and to properly load stiff, fast-action rods. So an 11-weight is a 12-weight according to the AFFTA standard, a Flats Pro labeled as an 8-weight is actually 240 grains, and so on., $120.

RIO InTouch Single Handed Spey 3D fly line

Why are Fly Lines Getting Heavier?

The InTouch Single Handed Spey 3D has a long 34-foot head that allows you to pick up and carry a longer line, which means you have to strip in less line before you cast, but you’ll also need some space for that D loop to lay out a full cast. The body and longer rear taper also give you the option of making a normal overhead cast, with better mending and line control after the line lands. RIO came out with the floating Single Handed Spey line in 2016. The new 3D version has three densities from the running line to the tip—floating, hover, and intermediate—to get your flies just under the surface. It’s perfect for swinging soft-hackles during a caddis hatch, or swinging streamers through a riffle without the tedious repetition of stripping in a bunch of running line before you can cast., $100.

Airflo Super-DRI Elite fly line

Why are Fly Lines Getting Heavier?

Most double-taper lines are symmetrical—identical at both ends. When you wear out one end, simply flip the line and you’ve got a brand new line. The Airflo Super-DRI Elite builds on this 2-in-1 idea with presentation tapers at both ends, but they are not identical. It’s an asymmetrical double-taper fly line. One end is tapered for delicate presentations, the other end is slightly more aggressive, with a thick tip taper to turn over bigger streamers, nymphs, and strike indicators. The 5-weight Super-DRI Elite is 145 grains, which is within the AFFTA standard. It’s perfect for fishing distances under 40 feet and standard-size drys and nymphs, but as the package indicates, don’t take this outside the trout world., $85.

Ed Jaworowski, with Bernard “Lefty” Kreh, is a creator of The Complete Cast: Applying Principles to Fresh and Saltwater Fly Casting. The 180-minute instructional film is available at

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