Brook trout are the wild jewels of cold, clean streams — compact, beautiful, and surprisingly heavy for their length. 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) = length cubed divided by 850 (length in inches). Brook trout are slightly deeper-bodied than rainbow or brown trout of the same length, which is reflected in the slightly lower divisor.
| Length | Average weight |
|---|---|
| 6″ | 0.25 lb |
| 7″ | 0.40 lb |
| 8″ | 0.60 lb |
| 9″ | 0.86 lb |
| 10″ | 1.18 lb |
| 12″ | 2.03 lb |
| 14″ | 3.22 lb |
| 16″ | 4.82 lb |
| 18″ | 6.85 lb |
Why brook trout stay small in many streams
In most native brook trout streams, the typical fish runs 6–10 inches. Brook trout are sensitive to water temperature and can only thrive in cold, highly oxygenated water — environments that tend to be lower in nutrients and food production. In these streams, a 12-inch brookie is a genuinely big fish. In larger, more fertile rivers and in lake-connected systems (where sea-run or lake-run “coasters” are possible), brook trout can grow to several pounds.
Wild vs. hatchery brook trout
Hatchery brook trout stocked into put-and-take fisheries are often heavier than wild fish of the same length, fed on pellets in a low-activity environment. Wild fish from fast, cold streams burn more energy and tend to be leaner. The chart above is most accurate for wild fish; stocked fish may run 10–15% heavier.
Get a weight tailored to your fish
For a more precise estimate, measure length and girth and use our free fish weight calculator — it applies the length-and-girth formula to account for how deep-bodied your individual fish is.