Fly Line Sink Rate and Rule Number Calculator Use FFR's basic calculator below to find the sink rate, rule number, and density of a fly line. Enter your own data into the blue cells and click the Calculate button.                       Enter fly line and water data.   Weight line wieght (grains per foot)     (Press Tab key to enter data.)   Diameter line diameter (thousandths of an inch)     ""   Temperature water temperature (degrees F)       Water water type: "f" for fresh, "s" for salt                     ""   Sink rate inches / second                     Rule number feet of line needed to deliver fly       to 1 foot hangdown depth in 3 mph water             Density ratio of line density to water density         (specific gravity)                         Sink rate and density calculations above are exact. Unless otherwise noted, rule number accuracy is within a few percent. Follow the links below for more information, including exact, pre-computed sink rate and rule number tables. Developed and validated by Tom Keelin, Bob Pauli and Jim Havstad. Additional FFR calculators include: a fly depth calculator to estimate fly depth at hangdown for various sink tips, lengths, and water conditions;  a tip length calculator to estimate length of sink tip required to deliver your fly to a given depth at hangdown; a sink tip converter to convert multiple sink tips of your choosing to equivalent lengths of a standard sink tip of your choosing;  and an Archimedes diameter calculator to find the diameter, sink rate, rule number, and density of a fly line when the most accurate measurements are desired. How this calculator works How to measure weight and diameter  Calculating diameter, rule number, and sink rate more accurately based on Archimedes' principle  Calculate fly depth for various sink tips, lengths, and water conditions Calculate sink tip length required to reach a given fly depth for various sink tips, lengths, and water conditions Sink rate lookup tables Rule number lookup tables Sink rate explanation and science Rule number explanation and science