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.

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.