The chart
The standard approved by the American Fly Fishing Tackle Association in 1960 numbers lines from 1 to 15, with 1 the lightest. Each number has a target weight, measured on the first 30 feet of line with any level tip left out. Here are the target weights for the numbers most anglers meet, as summarised by Wikipedia:
| Line weight | Target (grains) |
|---|---|
| 1 | 60 |
| 2 | 80 |
| 3 | 100 |
| 4 | 120 |
| 5 | 140 |
| 6 | 160 |
| 7 | 185 |
| 8 | 210 |
| 9 | 240 |
| 10 | 280 |
| 11 | 330 |
| 12 | 380 |
The same source lists a low and high figure around each target, about 6 grains either way at the lighter numbers. For example, a 5-weight falls between 134 and 146 grains. So "5-weight" means a range, not a point, and two 5-weight lines from different makers can differ slightly. The standard is a convention. It is not a law, and the number on the box is the maker's claim that the line sits within it.
A grain is a very small unit: the same source gives 100 grains as about 6.5 grams.
Why 30 feet
Wikipedia says the standard weighs the first 30 feet. A fly line is not a fixed-weight lure: the weight you are casting depends on how much of it is past the rod tip. Thirty feet is the agreed reference length, so a rod "loads" with 30 feet out. When you cast less than that you are casting fewer grains, and when you cast more you are casting more.
How to read the code on the box
Most makers write the line as taper, weight, buoyancy. Wikipedia gives WF-5-F as the example: weight-forward taper, for a 5-weight rod, that floats. Orvis writes the same idea as WF5.
- WF: weight forward, the most common taper per Orvis.
- DT: double taper, the same weight at both ends.
- F, S, F/S: floating, sinking, or a sinking tip with a floating running line.
Our types of fly line guide covers tapers and buoyancy in more detail, and the fly lines page shows the Line weight gauge, Taper, Floating / sinking and Length for each model, with "maker", "claimed", "listing" or "—" under each value.
How to choose
- Look at the rod. The weight is on the blank near the handle. Orvis says a 5-weight line casts best on a 5-weight rod because it is tapered for that rod.
- Start with a floating weight-forward. Orvis calls floating the most common line and a good beginner choice, and weight-forward the most common taper. A floating WF5 handles most fishing on a 5-weight trout rod.
- Check the water. Orvis recommends a sink-tip when you fish streamers in fast, heavy water, and a sinking line for still water such as lakes.
- Know the exceptions. Orvis says anglers can use mismatched weights, and suggests one size up when you need to throw a heavier fly such as a streamer, since a mismatched line may not turn over easily.
If you are still choosing a rod, our fly rod weight chart guide matches weights to fish, and rod pages such as 3-weight, 5-weight and 8-weight show what is listed.
Common mistakes
- Assuming heavier means thicker. A line's weight number is mass over 30 feet, not diameter.
- Buying the line by its look. Two lines with the same number can have very different tapers. The number is only the start.
- Forgetting the rod's own number. Check it on the blank before you buy a line.
- Treating one size up as a rule. It is a fix for heavy flies, not a habit.
The number on the box is a promise about 30 feet of line. Fish don't read spec sheets. You should.
Quick reference
- Match line number to rod number.
- Start with floating weight-forward unless the water tells you otherwise.
- Go one size up only for heavy flies.
- Remember the number is for the first 30 feet, so short casts load a rod less.
Questions people ask
What weight fly line do I need?
The one that matches your rod. Orvis says line selection should typically match your rod weight and the style of fishing, and that a 5-weight rod is designed to cast a 5-weight line. The rod's weight is printed on the blank near the handle. If you do not know the rod, our fly rod weight chart guide helps you pick a weight for the fish.
How do I determine fly line weight?
Read the box or the line spool: the code includes the number, for example WF5F. The standard is based on the weight of the first 30 feet of line, excluding any level tip, according to Wikipedia's summary of the AFFTA standard. You cannot tell by looking at the line, because line weight is about mass, not thickness.
What does WF5F mean on a fly line?
Wikipedia explains the usual naming pattern as taper, weight, buoyancy. WF-5-F is a weight-forward taper, recommended for a 5-weight rod, that floats. Orvis uses codes such as WF5 for weight-forward and 5-weight.
Can I use a different weight line than my rod?
Yes, with trade-offs. Orvis says anglers can use mismatched weights, and suggests relining one size up when you need to throw a heavier fly such as a streamer, since a mismatched line may not turn over easily. Casting best on the matched weight is the starting point.
Does fly line weight affect whether it floats?
No. Weight is the mass of the first 30 feet. Floating or sinking depends on the line's construction: Wikipedia says floating lines have air bubbles in the coating and sinking lines have tungsten or other heavy particles. See our types of fly line guide.
Save this guide for later
Sources
- Wikipedia: Fly line — accessed 2026-10-15
- Orvis: How do I choose a fly fishing line? — accessed 2026-10-15