AFTM Fly Line Scale

Weigh In with Fly Lines

I have a lot of fly lines, some brand new, that I have acquired over the years and I would like to make use of them. Is there a method I could use to identify their AFTM number, so that they can be matched up to the correct rod?
Phil Sawford

Hywel Morgan replies: Unfortunately there is no quick fix to this problem as it is impossible to determine a line’s exact weight rating just by looking at it or casting with it. You will have to get yourself an accurate set of digital scales that accurately weighs in grains (480 grains are equivalent to 1oz so you can see how accurate the scales need to be). To determine the line’s weight rating you will have to weigh the first 30 feet (or 10 yards) of the line and whatever this weighs will tell you what rod it will match. The chart below shows the various AFTM scales.

Fly lines can be weighed in grains to determine their line rating.

Fly lines can be weighed in grains to determine their line rating.

The only problem with this method comes if any of the lines are long belly lines, as they do not fit into this scale. The belly might be 12 yards long and to use this line properly you should have the whole belly outside the tip of the rod before releasing the line so that extra two yards will turn a 7wt on the above scale into an 8 or 9wt. So if there are any long belly lines in your collection weigh the entire belly even though it might be longer that 10 yards and this will match the line correctly to the rod

Line Weight Grains Tolerable Range
1 60 54-66
2 80 74-86
3 100 94-106
4 120 114-126
5 140 134-146
6 160 152-168
7 185 177-193
8 210 202-218
9 240 230-250
10 280 270-290
11 330 318-342
12 380 368-392

Grains are weighed over front 30 feet of line.

Reprinted with permission of Trout Fisherman magazine.


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