Wondering what your rainbow weighs? This rainbow trout length-to-weight chart gives a quick, scale-free estimate for trout in average condition — perfect for a fast photo and release.
Rainbow Trout length-to-weight chart
| Length | Average weight |
|---|---|
| 10″ | 0.34 lb |
| 12″ | 0.6 lb |
| 14″ | 0.92 lb |
| 16″ | 1.37 lb |
| 18″ | 1.95 lb |
| 20″ | 2.76 lb |
| 22″ | 3.67 lb |
| 24″ | 4.77 lb |
| 26″ | 6.06 lb |
| 28″ | 7.57 lb |
These values use weight (lb) = length³ ÷ 2,900 (length in inches) for a trout in good condition. Lake rainbows and steelhead carrying heavy girth often run heavier than the chart.
What’s an average rainbow — and what’s a trophy?
Stream rainbows most anglers catch run 10–18 inches and about 1–5 pounds. Lake-dwelling and sea-run (steelhead) fish go much larger, commonly to 20 lb. A wild rainbow over 5 pounds (or in the 18–24 inch range) is widely considered a trophy in inland waters. The IGFA all-tackle record is 48 pounds (Lake Diefenbaker, Saskatchewan, 2009) — but note that fish came from escaped, fast-growing farm-strain stock, so it reflects aquaculture genetics rather than a truly wild rainbow.
Put a number on your exact fish (worked example)
Weight (lb) = Length × Girth² ÷ 800
A 20-inch rainbow with an 11-inch girth comes out to 20 × 11 × 11 ÷ 800 = 3.0 lb, above the 2.76 lb chart average — a well-fed lake fish. Measure both and use the free fish weight calculator; see how to estimate a fish’s weight.
Why two rainbows of the same length weigh differently
A stream fish burning energy in current is leaner than a lake rainbow gorging on baitfish. Pre-spawn fish are heaviest; females slim down after spawning. Diet and habitat drive the difference, which is why girth beats length alone.
Where and when to find bigger rainbow trout
Rainbows want cool, clear, well-oxygenated water — riffle-and-pool streams and cold lakes, roughly 55–68°F. Adults over about a foot increasingly eat baitfish, so streamers and baitfish imitations produce bigger fish. Good to know: steelhead are simply the ocean-run form of the same species. ID by the pink-to-red lateral stripe and heavy black spotting on body and tail.
Rainbow trout weight FAQ
How much does a 20-inch rainbow trout weigh? About 2.75–3 pounds in good condition.
What’s a trophy rainbow trout? Over 5 lb (or 18–24 inches) in most inland waters.
Are rainbow trout and steelhead the same fish? Yes — steelhead are the sea-run form of the rainbow trout.
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