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Fish Weight Calculator

Estimate a fish's weight from its length and girth with the standard length-girth formula, and see how much the shape factor moves the answer.

in
nose to tail fork, tail pinched
in
around the widest part of the body
both length and girth
divisor in the formula
800 is the usual starting point

The estimate is the standard length-girth field formula: weight in pounds = length in inches × girth in inches squared ÷ shape factor, with 800 as the common divisor for a bass-like body. A larger factor describes a slimmer fish for the same measurements, so the table shows the same fish at 700, 800, 900 and 1000 rather than pretending one divisor fits every species. Measure length from the tip of the snout to the tail fork with the tail pinched, and girth around the widest part with the fins folded down; centimetres are converted exactly at 2.54 cm per inch. The result is an estimate that can be off by roughly a tenth either way, because condition, spawn, stomach contents and species are not modelled, and it is no substitute for a scale. Everything runs locally in your browser with no storage, uploads or network access.