The “Rule-of-4”

  Course subjects Home Leader classification Leader design Types of leaders Match leader & line Match leader & fly Match leader & rod Selecting leaders Leader troubles Leader materials Knots & leaders Slip ons Permanent butts Leader formulas "Rule of 4" Rules of thumb Hinge test   Courses Home Knots Equipment Fly Reels Fly Lines Leaders Fly Rods Insectology Flies Fish Casting Reference library Course map

   One effective tool to use in understanding the relationship between leaders and flies is the “Rule-of-4”.  It is a simple formula that is easy to remember and call upon to make quick decisions about what leader tippet to use with various sizes of flies.

This "formula" says to:

 Use a leader tippet size that is 1/4th the size of the fly you are using . . .

Or, conversely,

The fly to match your leader tippet should be equal to 4 times the tippet designation . . .

For example: for a size 8 fly, use a size 2X tippet; for a size 12, use a 3X tippet; size 16, 4X, etc.

As a general guideline, this formula gives us the upper limit of what tippet size to use; so generally speaking, we could go to a heavier tippet, but not use a lighter one.

(This “formula” ‘taint perfect, but the fish don't know it.)

  Previous topic  Giving the "hinge test" 

Leader Formula
(for the "technicians" among us)

The following is a formula for tying your own knotted, tapered leaders:

L = L_p  x .55 x (D_p² / D²)

Where:
L = length of new leader segment
L_p = length of the immediately preceding segment
D_p² = the diameter of the preceding segment squared
D² = diameter squared of the leader segment "L"

Ta da: "Length of the segment equals the length of the preceding segment multiplied by 55% of the diameter of the preceding segment squared, divided by the diameter of the segment squared."

Whew!