Brook trout are the wild jewels of cold, clean streams — compact, beautiful, and worth handling fast for a quick release. This brook trout length-to-weight chart gives average weights for wild brookies, so you can size up your catch without keeping it out of the water.
Brook trout length-to-weight chart
These figures use weight (lb) = length³ ÷ 2,700 (length in inches). Brook trout are slightly deeper-bodied than rainbow trout, so the divisor is a touch lower than for rainbows.
| Length | Average weight |
|---|---|
| 6″ | 0.08 lb |
| 7″ | 0.13 lb |
| 8″ | 0.19 lb |
| 9″ | 0.27 lb |
| 10″ | 0.37 lb |
| 12″ | 0.64 lb |
| 14″ | 1.02 lb |
| 16″ | 1.52 lb |
| 18″ | 2.16 lb |
What’s an average brook trout — and what’s a trophy?
Brook trout size is highly regional. In small native Appalachian headwater streams, a typical adult is only 6–10 inches and a 12-inch brookie is a genuine trophy. In larger rivers, lakes, and northern (Canadian) systems — including lake-run “coasters” — they reach several pounds, and there an 18-inch or 3–5 lb fish is the trophy mark. The IGFA all-tackle record is 14 lb 8 oz, caught in Ontario’s Nipigon River in 1915 — one of the oldest records in the sport (some accounts say the fish was even heavier before the long trip to be weighed).
Put a number on your exact fish (worked example)
Because brook trout size varies so much by water, girth is the honest way to weigh yours:
Weight (lb) = Length × Girth² ÷ 800
A wild 12-inch brookie with a 7-inch girth works out to 12 × 7 × 7 ÷ 800 = 0.74 lb — a bit above the 0.64 lb length-only average for a hard-bodied stream fish. Measure both and use the free fish weight calculator for a number that fits your fish, not just its length; see how to estimate a fish’s weight.
Wild vs. hatchery brook trout
Hatchery brookies raised on pellets in low-activity tanks are often 10–15% heavier than wild fish of the same length. Wild fish from fast, cold streams burn more energy and run leaner — another reason to trust girth over a length-only average.
Where and when to find bigger brook trout
Brook trout are the most cold- and clean-water-demanding of the common trout — clear, cold, well-oxygenated streams and lakes around 55–60°F, with shade, cover, and clean gravel. They die off in sustained water above ~72°F, which makes them an indicator of pristine water. Bigger fish live in larger, more fertile rivers and lake systems. ID: unmistakable worm-like (vermiculate) markings on the back, red spots with blue halos, and white-edged lower fins.
Brook trout weight FAQ
What’s a trophy brook trout? In small streams, 12 inches; in big rivers/lakes, 3–5 lb or 18+ inches.
Why are stream brook trout so small? Cold, clean water tends to be low in nutrients, so growth is slow — a 10-incher can be several years old.
Is a brook trout really a trout? Technically it’s a char, a close relative — but it fishes and tastes like the trout everyone knows.