Fish Weight Estimator
Weigh your catch without a scale. Enter length — and girth if you measured it — to estimate a fish's weight with the standard angler formulas, then get it back in the water fast.
Weigh, record, release
The healthiest way to handle a good fish is to measure it, estimate the weight, snap a photo, and slip it back — no hanging it on a scale by the jaw. A quick length, and a girth if you can manage it, is all these time-tested formulas need to give you a number for the logbook while the fish stays wet and stress stays low.
Heading out for a specific species? Set up the right rod with the Rod Power & Action Guide and the right line with the Fishing Line Strength Selector.
Frequently Asked Questions
How do you estimate a fish's weight from measurements?
There are two standard methods. The more accurate one uses length and girth: weight in pounds equals length times girth squared, divided by 800, with both measured in inches. If you only have length, the estimator uses a species-specific shape factor — weight equals length cubed divided by that factor — which accounts for how heavy-bodied the species is. A fat carp and a slender pike of the same length weigh very differently.
Why does including girth make it more accurate?
Length alone can't tell a lean fish from a fat, pre-spawn one of the same length. Girth captures that body condition directly, which is why the length-times-girth-squared formula is the one tournament and record circuits lean on. If you can wrap a tape around the fattest part of the fish before release, do it — the estimate tightens considerably.
How accurate is the estimate?
Consider it a good approximation, not a certified weight. Real weight varies with the season, how recently the fish fed, spawning condition, and natural variation between individuals. Even the girth formula can be off by a fair margin on an unusually fat or thin fish. It's ideal for a quick catch-and-release record; for anything official you still need a certified scale.
Can I estimate weight for any species?
The estimator carries shape factors for common freshwater and inshore game fish — bass, trout, salmon, walleye, pike, muskie, panfish, catfish, carp, redfish, and striped bass. Pick the closest match. If you have girth, the length-and-girth method works reasonably across species regardless, because it measures the fish's actual body rather than relying on a species average.
An estimate from standard formulas, not a certified weight. Real weight varies with condition and season — use a certified scale for any official record.