Flatheads are heavy, stocky brutes that pack on weight fast, so length tells you a lot about a big cat. This flathead catfish length-to-weight chart estimates weight from length so you can size up a bruiser before the release.
Flathead catfish length-to-weight chart
| Length | Average weight |
|---|---|
| 14″ | 1.22 lb |
| 16″ | 1.82 lb |
| 18″ | 2.59 lb |
| 20″ | 3.56 lb |
| 22″ | 4.73 lb |
| 24″ | 6.14 lb |
| 26″ | 7.81 lb |
| 28″ | 9.76 lb |
| 30″ | 12.00 lb |
| 32″ | 14.56 lb |
| 34″ | 17.47 lb |
| 36″ | 20.74 lb |
| 40″ | 28.44 lb |
| 44″ | 37.86 lb |
These figures use weight (lb) = length³ ÷ 2,250 (length in inches), calibrated to Missouri Department of Conservation data from over 6,000 measured flatheads.
What’s an average flathead — and what’s a trophy?
A common “eater” flathead runs 15–28 inches and 1–10 pounds, while dedicated flathead anglers target 24–36 inch fish (roughly 6–25 lb). Anything past the mid-30-inch mark is a notable catch. Anglers widely treat 30 pounds as the trophy threshold — 20 lb is a strong fish and 50 lb+ is a true giant (a convention, not an official mark). The IGFA all-tackle world record is a massive 123 pounds, caught at Elk City Reservoir, Kansas, in 1998.
Put a number on your exact fish (worked example)
Flatheads are broad, heavy-bodied fish, so girth adds up fast:
Weight (lb) = Length × Girth² ÷ 800
A 36-inch flathead with a 24-inch girth works out to 36 × 24 × 24 ÷ 800 = 25.9 lb, well above the 20.7 lb length-only average — a thick, well-fed fish. Measure both and use our free fish weight calculator; see how to estimate a fish’s weight.
Why two flatheads of the same length weigh differently
Flatheads eat almost exclusively live prey, which drives fast, heavy growth — a reservoir fish gorging on shad and sunfish runs much stouter than a river fish of the same length. Pre-spawn females are heaviest; guarding males feed little during nesting and can slim down in midsummer.
Where and when to find bigger flathead catfish
Flatheads hold in deep, slow pools of big rivers, reservoirs, and lakes — turbid water with heavy structure like logjams, timber, undercut banks, and rock. They’re solitary and territorial, tucking into deep cover by day and moving shallow to feed after dark. Gear tip that matters: flatheads want it alive. Unlike other catfish, adults rarely scavenge — the go-to is a large live baitfish (bluegill or sunfish where legal, shad, bullhead) fished on the bottom tight to cover at night.
Flathead catfish weight FAQ
How much does a 30-inch flathead weigh? About 12 pounds in average condition.
What’s a trophy flathead catfish? Roughly 30 lb; 50 lb+ is a true giant.
Do flatheads bite dead or cut bait? Occasionally, but adults strongly prefer live prey — live bait tight to cover is far more productive.
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