Landed a buttery-gold brown and want to know its weight? This brown trout length-to-weight chart estimates weight from length for a fish in average condition — handy for a quick photo-and-release on wild trout water.
Brown trout length-to-weight chart
| Length | Average weight |
|---|---|
| 10″ | 0.40 lb |
| 12″ | 0.69 lb |
| 14″ | 1.10 lb |
| 16″ | 1.64 lb |
| 18″ | 2.33 lb |
| 20″ | 3.20 lb |
| 22″ | 4.26 lb |
| 24″ | 5.53 lb |
| 26″ | 7.03 lb |
| 28″ | 8.78 lb |
These figures use weight (lb) = length³ ÷ 2,500 (length in inches), calibrated to statewide average-condition data (Pennsylvania Fish & Boat Commission). Well-fed lake and tailwater browns run heavier.
What’s an average brown trout — and what’s a trophy?
Most stream browns run 10–16 inches and about ½ to 2 pounds, with a good wild fish being 14–18 inches; lake, tailwater, and Great Lakes browns grow far larger. Anglers widely treat 20 inches or about 5 pounds as a trophy stream brown, pushing the bar to 10 lb+ on big water (an angler convention, not an official standard). The IGFA all-tackle record is 44 lb 5 oz from New Zealand (2020) — a pellet-fattened canal fish — while the classic North American benchmark is the roughly 40-pound brown from Arkansas’s Little Red River in 1992.
Put a number on your exact fish (worked example)
Length-only charts can’t tell a lean insect-eater from a predatory brown that’s been eating baitfish. Girth can:
Weight (lb) = Length × Girth² ÷ 800
A 20-inch brown with a 12-inch girth works out to 20 × 12 × 12 ÷ 800 = 3.6 lb, above the 3.20 lb length-only average — a well-fed fish. Measure both and use our free fish weight calculator; see how to estimate a fish’s weight.
Why two browns of the same length weigh differently
Big browns turn strongly predatory — a fish gorging on sculpins and minnows gets deep and heavy, while an insect-eating stream fish stays lean. Fall pre-spawn females are the heaviest of the year, and post-spawn winter fish are leaner at the same length. Tailwater and lake browns simply outweigh stream fish of equal length.
Where and when to find bigger brown trout
Brown trout live in cool, clean, well-oxygenated streams, tailwaters, and lakes around 53–66°F — and they tolerate warmth better than brook or rainbow trout. They hold near undercut banks, cover, and current breaks and feed hardest at low light, so early, late, and after dark produce the biggest fish. Fall, as pre-spawn browns get aggressive and territorial, is prime trophy season. ID: black and red/orange spots (the red ones often ringed with a blue halo) on a brown-gold body, and a nearly spotless tail — the fastest way to separate a brown from a rainbow or brookie.
Brown trout weight FAQ
How much does a 20-inch brown trout weigh? About 3 to 3.6 pounds, depending on how well-fed it is.
What’s a trophy brown trout? Roughly 20 inches or 5 lb on a stream; 10 lb+ on lakes and tailwaters.
Why are lake and tailwater browns so much heavier? They switch to eating baitfish and grow deep, heavy bodies that beat length-only averages.
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