Fish Weight Calculator

Formulas have long been developed in freshwater and saltwater for using length and girth to estimate the weight of a fish, and these have been evolving since the days (at least the 1940's) when a formula for fish with a cylindrical body shape was applied to all fish, although this didn't take into account especially elongate or round species.

In all cases you need to know the length. To make measurements, use a soft tailor's tape measure or a piece of marked cord or thin-diameter rope that will not shrink and is marked at regular intervals. In a pinch, you can measure small fish by spreading your fingers and using the distance from pinky to thumb. Another emergency measure is to use your fishing rod, aligning the butt with the tip of the fish's jaw. Still another is to cut nylon line off the reel and cut it to the exact length (and girth) of the fish.