🎣 Fish Weight Calculator
Enter a fish's species and length — and its girth if you have it — to estimate its weight in pounds and kilograms before you ever reach for a scale.
🐟 Estimate Your Catch
What is a Fish Weight Calculator?
A fish weight calculator turns a quick tape measurement into a weight estimate, so you can log a catch or photograph and release a fish without hauling a scale to the water. Length alone gives the species' published standard weight; length plus girth uses the anglers' girth formula. Log either one as an estimate, never as a weight.
Pick your species, measure carefully, and add girth whenever you can for the most accurate result. Treat the number as a field estimate: a certified scale is the final word.
❓ Frequently Asked Questions
How do you estimate a fish's weight from its length?
Most species follow a predictable length-to-weight relationship. With length alone, the calculator gives the species' standard weight from its published length-weight equation (for example Henson (1991) for largemouth bass): the weight a fish of that length reaches in good condition, so most fish of that length weigh less. A heavy-bodied bass and a long, lean pike of the same length weigh very differently. For any other species, add a girth.
Does adding girth make the estimate more accurate?
Yes. A girth measurement captures how full-bodied an individual fish is, which length alone can't. When you supply girth, the tool switches to the standard girth formula — girth squared times length, divided by 800 — which accounts for fat, pre-spawn, or trophy fish that are heavier than their length suggests.
How should I measure the fish?
Measure total length from the tip of the nose to the end of the tail along a flat surface, in inches. For girth, wrap a soft tape around the fattest part of the body, just ahead of the dorsal fin. Measure quickly, keep the fish wet, and release it promptly if you're practicing catch and release.
Is this accurate enough for a record or tournament?
No. These formulas give a good field estimate for fun and for catch-and-release logging, but they are approximations. For an official record, tournament weigh-in, or anything that needs to be exact, use a certified scale.