With most of us practicing catch and release fishing these days — and avoiding hanging a fish from a damaging gripping/weighing device, we need some way to calculate the approximate weight of a fish. Well there is a formula that is commonly used which, while not as accurate as actually weighing the fish on a scale, at least gives one some idea of what the fish weighs.
The Formula is this:
(Girth x Girth) x Length) / 800 = weight in pounds
(girth and length are inches)
If the girth of a fish is 12 inches and the length is 24 inches, the formula would be used as follows:
12 x 12 x 24, divided by 800 = 4.32 pounds