Short answer: match the line weight to the number printed on your rod blank, pick a weight-forward floating taper if you're unsure, and stop there. Grain weight, taper profile, and coating all matter — but not until you've fished long enough to know what you're trying to fix.

Floating lines are versatile and one of the more common line types anglers consider. They're especially popular with beginners, and at each stage it feels like you know just enough more to confuse yourself. In the past ten years there has been more advancement in fly lines than almost anywhere else in the sport, and the manufacturers have muddied the water by varying weights, grains, and standards. Rather than add to the confusion, let's boil the ocean and sort this into a few buckets.

What is grain weight?

In fly fishing, grain weight refers to the weight of the fly line's first 30 feet, except for level line. It's measured in grains — and for perspective, there are about 440 grains in an ounce.

Grain weight is crucial because it has to match your rod's weight rating. That's what makes the line load the rod correctly when you cast, giving you the right amount of flex and power to present your fly.

Here's the wrinkle: manufacturers have started overweighting lines to make rods flex more and cast easier. For years anglers were doing this manually, so now when you "overline" by moving up a grain weight yourself, you're really overlining — because the manufacturer already did it for you. You can see how quickly this gets out of hand.

New fly fishing lines being spooled onto a set of fly reels

Grain weight standardization

The governing body for standardising fly line weights is the American Fly Fishing Trade Association (AFFTA). They provide a standardised system for weight specifications, ensuring consistency across manufacturers.

The AFFTA standard uses a numbered scale, and each number corresponds to a specific grain range for the first 30 feet of line, excluding the level tip. This helps you match line to rod for optimal performance.

The table below shows the AFFTA standards alongside the other variables that actually affect your choice — rod action, common uses, taper, density, coating, and conditions. I've included all of them so you can see that a single "perfect line" for a rod doesn't really exist. It's a range, and how the line and rod feel working together is ultimately defined by you. The ease and effectiveness of accomplishing what you set out to do is the real goal.

Line Wt	Grain Range (first 30ft)	Matching Rod	Rod Speed	Common Uses	Taper	Density	Coating	Conditions
1	60-74	1-weight	Soft-action	Delicate dry fly, small streams	WF, DT	Floating	Standard, hydrophobic	Calm, clear water
2	75-89	2-weight	Soft to medium	Small trout, precise casting	DT, WF	Floating	Standard, hydrophobic	Calm, clear water
3	90-104	3-weight	Medium	Light nymphing, small to medium streams	DT, WF	Floating	Standard, hydrophobic	Calm to moderate currents
4	105-119	4-weight	Medium to medium-fast	Small to medium streams, dry/nymph combo	WF, DT	Floating	Standard, hydrophobic	All-around
5	120-134	5-weight	Medium-fast	All-around trout, general freshwater	WF	Floating	Enhanced slickness	Variable
6	140-152	6-weight	Fast	Larger trout, small bass, light saltwater	WF	Floating, sink tip	Slickness, durability	Wind, larger flies
7	153-168	7-weight	Fast	Bass, carp, light steelhead	WF	Floating, sink tip	Durability, tactile	Varied, light saltwater
8	169-185	8-weight	Fast to very fast	Saltwater, steelhead, salmon	WF	Floating, sink tip, full sink	Saltwater treatment	Coastal, windy
9	186-202	9-weight	Very fast	Heavy saltwater, stripers, pike	WF	Floating, sink tip, full sink	Saltwater, tactical	Rough, open water
10	203-219	10-weight	Very fast	Big game saltwater, tarpon	WF	Floating, sink tip, full sink	Saltwater, high durability	Tropical, heavy wind
11	220-236	11-weight	Extra fast	Large tropical species, offshore	WF	Floating, sink tip, full sink	High durability, tactile	Offshore, heavy flies
12	237-253	12-weight	Extra fast	Largest tropical species, billfish	WF	Floating, sink tip, full sink	High durability, saltwater	Extreme conditions

The table is truncated here for readability, but the AFFTA scale continues up to 15-weight.

Adjusting for rod action

These guidelines assume a standard medium-action rod. Here's how to adjust:

Slow action rods often cast better with a line at the lower end of the grain range, or even one weight lighter. The slower recovery allows what feels like a deeper bend and therefore needs slightly less weight. Think of a soft dry fly rod that doesn't whip your cast and slap the line to the water. These full-flex rods bend deeply, almost to the handle.
Medium action rods typically stick with the AFFTA standard. They give you a bit of both worlds — soft presentation, yet enough power to generate line speed and cut wind. These mid-flex rods bend to about the halfway point.
Fast action rods may benefit from the higher end of the grain range, or even one weight heavier, to fully load the rod. Read the box carefully — there are often small details outlining grain overages. Overloading generates a lot of line speed but takes more energy and better timing. These tip-flex rods bend primarily in the top third, and the additional weight pushes the flex point deeper into the blank, which is where the power comes from.

Three other variables worth understanding:

Taper is the profile of the line and affects how energy transfers during the cast. Weight forward is great for distance and wind; double taper is more delicate and can be reversed for extended life.
Density determines whether the line floats or sinks. Floating lines are the most common, but sink tips and full sinking lines are crucial for fishing deeper water.
Coating can repel water, enhance slickness for easier casting, or add durability for abrasive saltwater. More and more manufacturers are now adding textures as well.

How grain weight interacts with your rod

Imagine a dance between your line and your rod. The grain weight leads the steps and the rod follows. If the line is too heavy it overloads the rod, making it flex too much, which makes casting less accurate and feel cumbersome. Too light and the rod won't flex enough, giving you poor mechanics and less power.

The key is finding a grain weight in harmony with your rod's rating. That synergy gives you smooth, efficient casts and better control over presentation.

Four common misconceptions

"Grain weight is the same as rod weight." Not quite. Rod weight indicates the class of line the rod is designed to cast optimally. Because of personal preference and different rod actions, some anglers deliberately choose slightly heavier or lighter.

"More grain weight means longer casts." Heavier doesn't always mean farther. A heavier line can carry more energy, but if it isn't matched to the rod it will hurt both distance and accuracy.

"Grain weight determines the sinking rate." That's specific to sinking lines. For floating lines, grain weight won't affect how it floats — though the distribution of weight along the line affects how it sits on the water and how easily you can mend it.

"Any line weight works on any rod." Not recommended. A grain weight unsuited to your rod makes casting difficult and can risk damaging the rod.

Types of floating fly line

Weight Forward (WF) is heavier at the front, so it shoots further and easier — like a slingshot. Good for distance and wind, and the easiest to cast, which makes it the best starting point for a beginner. The trade-off is a slightly heavier landing, which you can soften with your casting stroke.
Double Taper (DT) is even at both ends and thinner in the middle. Nice for gentle presentation at shorter range, and you can reverse it when one end wears out.
Level (L) is the same thickness throughout. Simplest and cheapest, but nowhere near as easy to cast.

Materials

PVC with additives is the most common. Plastic blended with ingredients that help it float and stay supple.
Polyurethane is tougher across temperature extremes — a jacket that's good for all seasons rather than one.
PVC-free lines skip the PVC for materials kinder to the environment. They work well but usually cost a bit more.

So which line should you actually buy?

I'm assuming you're now more confused than when you started, so here's the practical version. Look at your rod's speed and action. Find your position in the grain range. Decide whether you want longer casts or normal casting lengths. Then consider coating, texture, and the conditions you fish.

Here's what that maps to in our shop:

If you're buying your first line

A weight-forward floating line matched to your rod weight. The Moonlit Performance WF Taper Floating or the Moonlit WF All-Purpose are both exactly this, and the Classic Taper WF Floating is another solid option. The Perfect Taper Sky is worth a look because the two-tone colour change shows you exactly where your head ends — genuinely useful while you're learning to feel the load.

If you fish technical dry fly water

A Double Taper Floating Line. Softer presentation at short range, better roll casting, and you get a second life out of it by reversing the spool.

If you need to get deeper

This is where most anglers are leaving fish uncaught. Sink tips float the running line and sink only the front section, so you can still mend and control the drift. Choose by rate rather than by name: S1 intermediate for shallow water and just under the film, S3 medium for swinging streamers in moderate current, and S5 fast for deep runs and heavy current.

For stillwater where fish are holding deep, a Full Sinking Fly Line, Alpha II Sinking, or Alpha SS takes the whole line down.

If you fish salt

Saltwater lines use stiffer cores that don't go limp in tropical heat, which is exactly the failure mode of a freshwater line on the flats. The Moonlit WF Saltwater or the Silvertip Saltwater WF.

If you throw big flies for bass or pike

A short, aggressive head turns over air-resistant flies that a trout taper simply won't. The Bass Taper in Moss or the 9wt Yellow.

Don't forget backing and leaders

Backing fills the arbor so your fly line sits at a wider diameter, which reduces memory and coiling, and gives you reserve if a fish runs past the fly line. See leaders and backing and tippets.

Browse the full fly lines collection.

A note on how to decide

When you're working through this, write it down in your own table with notes. Review it, ask questions of someone who knows, and go for it. Every line will teach you something, and with the guidelines above you'll have no trouble selecting one you're happy with and understanding the system you built.

Individual casting style and conditions might lead you to prefer slightly lighter or heavier than standard. Your speed, timing, strength, and experience all have dramatic effects on how a cast performs — an extremely light presentation can absolutely be made with a fast action rod. What I've found is that most anglers prefer the rod style they learned on, because muscle memory is strongest there.

My tip: practice with varying degrees of rod and line, and concentrate on feeling the flex while performing the task at hand.

And don't forget the most important part — it isn't the line or the rod. It's you and your casting. A good cast will help you far more than any purchase. Read the Formula for Systematizing Your Cast and Part 1 of Become a Better Angler next.