Estimate a fish’s weight from its length using published length–weight relationships for common species, with a girth-based cross-check.
Estimated weight
How to use this tool
Choose from the listed species; unlisted species are not guessed.
Total length, in centimetres or inches.
In advanced options, for an independent girth-based estimate.
Weigh the fish on a scale for records, tournaments or regulations.
Formula & worked example
A 50 cm largemouth bass is estimated at 1462 g (3.22 lb) from W = 0.010 · L^3.04.
Limitations — read this before you rely on it
Estimates only, for listed species in average condition. Season, sex, spawning state and local populations shift real weights; never use for legal size or bag-limit decisions.
Frequently asked questions
Within roughly ±20% for a fish in average condition; fat, spawning or thin fish fall outside that.
Weight grows roughly with the cube of length, so one equation covers all sizes for a species.
It is not guessed. Use the closest listed species only as a rough guide and label it as such.
The angler’s rule weight(lb) = length(in) × girth(in)² / 800 — a useful cross-check when you measured girth.
These relationships use total length; fork length gives a slightly lower estimate.