How to Match Fly Line Weight to an Unmarked Rod

Each fly rod is designed to cast a specific weight of fly line. A mismatched fly rod and fly line can make for a long, frustrating day of fishing. Fly lines come in a variety of weights, ranging from 1 to 14, with 1 being the lightest weight option. Fly rods are typically marked with this weight to make matching easier. You can test unmarked rods by using the Common Cents System developed by Dr. William Hanneman to determine its weight.

Things You'll Need

  • Flat surface
  • Books
  • Tape measure
  • Pen and paper
  • Paperclip
  • Plastic bag
  • Pennies
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Instructions

    • 1

      Place the fly rod on a flat surface. Arrange the rod so that the eyelets of the rods are facing upwards. Use books to keep the rod in place.

    • 2

      Measure the distance from the floor to the fly rod. Write down this distance.

    • 3

      Measure the length of the fly rod from the butt of the rod to the tip. Divide this number by three to determine one-third of rod length. For example, if the rod is 102 inches long, one third of the length is 34 inches.

    • 4

      Subtract the height and one-third of the rod length. This number will indicate how much the tip of the rod needs to bend to measure its overall Effective Rod Number, or ERN. For example, if the height is 64 inches and one-third of the rod length is 34 inches, and 64 minus 34 equals 30 inches. This is the distance from the floor that the rod tip needs to reach to determine its ERN.

    • 5

      Add a paperclip to the end of the rod. Attach the plastic bag to the other side of the paper clip.

    • 6

      Add pennies into the bag to weigh down the tip of the fly rod. Continue adding pennies until the rod tip reaches the distance from the floor determined in Step 4. In our example, that would be 30 inches.

    • 7

      Multiple the number of pennies by 38.61, which is the weight in grains each penny weighs. This number indicates the total number of grains the rod can support when fully loaded.

    • 8

      Use the Relationship of Rod Intrinsic Power to AFTMA Line Number chart to match the weight in grains to determine the ERN number. For example, a rod that supports 2000 grains is an ERN 6.

    • 9

      Select the fly line weight that is the same size as the ERN listed on the AFTMA line chart from step 8. So if the ERN of the rod is a 6, then select a fly line weight of 6. The AFTMA created the weights of rod to fly line numbers to be equal to one another to avoid confusion when shopping for fly line and rods.