Tools you might need next
Calculate fishing line strength and leader size for target species, technique, and drag setting based on line type and test rating.
Calculate optimal trolling speed in mph and knots for target fish species, lure type, and desired lure running depth on lakes or oceans.
Compare fishing knot breaking strength as a percentage of line rating for Palomar, Uni, FG, and other popular terminal connections.
Many freshwater formulas cube length and multiply by girth squared with a species constant.
weight (lb) ≈ (girth² × length) / K (K varies by species shape)Slim trout use higher K than deep-bodied bass or panfish. Select the shape closest to your catch.
Length is usually total length tip to tail. Girth is maximum circumference usually ahead of the tail.
Updated: July 2026
Estimate bass weight from a quick girth and length before release when scales are not allowed.
Confirm a walleye or snook is above minimum weight from board measurements.
Compare estimated weight of similar-length species with different body depth.
Use the same total-length standard your regulation or formula expects, often tip of snout to tail tip.
Body shape changes the constant. Pick species-specific or general shape category.
Weigh your catch with a tape measure. Enter total length, girth, and species type to estimate weight using standard fisheries formulas.