Catfish weight calculator for channel catfish

Which equation is this, and why that one?

The calculator runs the channel catfish standard-weight equation published by Brown, Murphy and Springer in the Journal of Freshwater Ecology in 1995:log10(Ws) = −5.8 + 3.294 × log10(TL), grams and millimetres.

Two things make it the right choice. It was fitted across 241 separate channel catfish populations, so it is not a single lake's quirks dressed up as a law. And it replaced an earlier equation that only worked from 280 mm upward — the 1995 revision pushed the valid range down to 70 mm, which matters if you are logging the small fish as well as the ones worth a photograph.

The exponent of 3.294 is the highest of the three species this site covers. In practice that means a channel catfish puts on weight faster per inch than a walleye does, which is why the 30-inch fish in the table below is nearly twice the weight of the 24-inch one despite being only a quarter longer.

Where does this weight data come from?

The length-to-weight curve is the Brown, Murphy and Springer (1995) channel catfish standard-weight equation, held in the Fisheries Stock Assessment standard-weight database. Relative-weight presets (lean Wr 85, typical Wr 100, heavy Wr 115) are the same condition bands fisheries crews use when they score a sample. Every figure on this page is a sourced value with a verification date; the full list is on ourresearch methodology page. If a citation cannot be re-checked, the build fails and the number does not ship.

What works for channel catfish on the Mississippi River?

On this stretch the productive water is the Lock and Dam 8 tailwater and the deeper holes along the main channel, not the flooded timber where bass live. Cut bait and a stout rod matter more than a fancy estimate, but once a fish is in the net the tape is what you trust — not the landing-net guess. ThePool 8 fishing near Genoa covers the ramps, the four-fish walleye bag you will share the tailwater with, and the current that makes a light spool a bad idea.

What does a channel catfish weigh at each length?

Three columns, because one column would be a lie. Lean is a fish that has just spawned or has been holding in cold tailwater without feeding; Heavy is a fish stuffed with shad in October.

The 30-inch row is the one worth memorising if you fish the Upper Mississippi. That is roughly the size at which a channel catfish stops being a nice fish and starts being a story, and the honest spread across condition classes is 9.3 to 12.5 pounds. Anyone who tells you a 30-inch channel cat is "a solid twelve" is describing the top of that range, not the middle.

Two worked examples from Pool 8 and Pool 9

Both examples are lengths we actually see on the Upper Mississippi. For a walleye from the same tailwater, switch to thewalleye weight calculator — the equations are not interchangeable.

A 28-inch fish from the Lock and Dam 8 tailwater in June

28 in is 711.2 mm. The log of 711.2 is 2.85199; multiplied by 3.294 that is 9.39445; subtract 5.8 and you have 3.59445, so Ws = 3,931 g, which is 8.67 lb. June fish in the tailwater are usually pre-spawn or actively spawning and run a little heavy, so at 115 relative weight the estimate is 9.97 lb with a range of 9.10 to 10.83.

A 20-inch fish from a backwater slough in late August

20 in is 508 mm and the equation returns 1,298 g, or 2.86 lb at typical condition. Late-August backwater fish that have been on a shad diet often measure heavy: 3.29 lb, range 3.00 to 3.58. If the same fish came out of a cold, high-water spring when nothing was feeding, the lean setting gives 2.43 lb. That is a difference of nearly fourteen ounces on one length, which is the whole argument for having a condition control instead of a single lookup.

What do catfish anglers get wrong here?

The species mix-up is far and away the biggest one. Channel catfish, flathead catfish and blue catfish look similar enough on a phone screen that people apply one number to all three. The tail settles it: a channel catfish is deeply forked, a flathead is squared off. If the tail is square, close this page — the answer it gives you will be too light, sometimes by several pounds on a big fish.

Second is fork length. Because the tail is so deeply forked on this species, the gap between fork length and total length is larger than on most fish, and the error runs one way only: always too light.

Third is trusting a summer number in spring. Channel catfish on the Upper Mississippi lose real condition over winter and through the post-spawn window, and a fish that measured heavy in October can measure lean in May at the same length. Use the condition control rather than assuming the middle column.

Fourth, and this one costs money rather than accuracy: people size their reel to the fish rather than to the line. If you are moving up to heavier line for big cats, run the numbers on theline capacity calculator first, because a spool rated for 300 yards of 12 lb mono holds far less 30 lb mono than the label suggests.