🐟 Rainbow Trout Length to Weight Calculator
Estimate your rainbow trout's weight from length & girth — imperial or metric
| Length (in) | Length (cm) | Est. Weight (lb) — Standard | Est. Weight (kg) | Trophy Class |
|---|---|---|---|---|
| 8" | 20.3 cm | 0.22 lb | 0.10 kg | — |
| 10" | 25.4 cm | 0.44 lb | 0.20 kg | — |
| 12" | 30.5 cm | 0.75 lb | 0.34 kg | — |
| 14" | 35.6 cm | 1.22 lb | 0.55 kg | — |
| 16" | 40.6 cm | 1.83 lb | 0.83 kg | — |
| 18" | 45.7 cm | 2.62 lb | 1.19 kg | — |
| 20" | 50.8 cm | 3.61 lb | 1.64 kg | 🌟 Trophy |
| 22" | 55.9 cm | 4.83 lb | 2.19 kg | 🌟 Trophy |
| 24" | 61.0 cm | 6.30 lb | 2.86 kg | 🏆 Elite |
| 26" | 66.0 cm | 8.06 lb | 3.66 kg | 🏆 Elite |
| 28" | 71.1 cm | 10.12 lb | 4.59 kg | 🥇 Record Class |
| 30" | 76.2 cm | 12.51 lb | 5.68 kg | 🥇 Record Class |
| Habitat / Type | Condition Factor (K) | Body Shape | Typical Weight vs. Length |
|---|---|---|---|
| Wild Mountain Stream | 0.88–0.95 | Slender, torpedo | Lighter than average |
| Productive River / Tailwater | 0.95–1.05 | Well-proportioned | Average weight |
| Lake / Reservoir | 1.00–1.10 | Deeper bodied | Slightly above average |
| Hatchery Stocked | 1.10–1.25 | Rounder, heavier | Above average (feed pellets) |
| Post-Spawn (any) | 0.75–0.88 | Very thin, gaunt | Well below average |
| Steelhead (sea-run) | 1.05–1.20 | Thick, muscular | Well above average |
| Formula Type | Formula | Accuracy | Best Used When |
|---|---|---|---|
| Length + Girth (Standard) | L × G² ÷ 800 | ★★★★★ Excellent | You have a tape measure |
| Length Only (Power Law) | K × L³·⁵ ÷ 10,000 | ★★★ Good | Quick field estimate |
| Length Only (Simple Cubic) | L³ ÷ 2,700 | ★★ Fair | Rough ballpark only |
| Metric (Length + Girth) | L(cm) × G(cm)² ÷ 27,800 | ★★★★★ Excellent | Metric measurements |
| Condition Factor (K) | W(g) ÷ (L(cm)³ ÷ 100) | ★★★★ Very Good | Fish health assessment |
rainbow trout range a lot in weight according to the place where the fish live and how they grow. Trout in freshwater brooks usually have weight between 0.5 and 2.5 kilos, which is around 1 to 5 pounds. Forms that live in lakes can reach much bigger weight up to 9 kilos or around 20 pounds.
Typical weight for the species falls between 2 and 8 pounds where 8 pounds is quite common for a well-growing adult.
How Big Are Rainbow Trout
rainbow trout normally measure between 20 and 30 inches. The length can range from only 8 inches to almost 24 inches, depending on the particular fish. The height of the body falls between around 4.5 and 7 inches.
Maximum weight reaches around 10 kilos, but most of them weigh form 1 to 4 kilos.
Steelhead is simply the same species as rainbow trout, only in a migratory form. They can reach 40 pounds or even more, although the usual weight is between 8 and 11 pounds. There are reports about steelhead that weighed up to 55 pounds.
Normal length is 18 to 24 inches, but won mentioned cases with 45 inches. That makes them truly impressive big fish.
Trout grown on farms are hard to exactly describe. Their weight can go from 2 to 16 pounds. The typical length stays in the range of 20 to 30 inches.
Some rainbow trout reach more than 10 pounds, and fish of 10 to 12 pounds would be a brilliant catch. Everything above 5 pounds counts as big, while trout over 10 poundscommonly get called monsters.
In 2009 someone officially caught the biggest rainbow trout in Canada, that weighed 48 pounds. It came from Lake Diefenbaker in Saskatchewan. A fisher also caught a 29.8-pound rainbow trout from the Kootenay River, but it did not beat the prior record of 33.1 pounds.
A 15-pound rainbow trout was caught at Clear Lake beside Mountain Hood in Oregon, with length of 31 inches.
Guessing the weight of fish only looking at it is a real challenge. A common method is to halve any big guess. It is true that there is a clear formula for finding the weight.
You multiply the length by the square of the girth, then divide by 800. For instance, a 20-inch fish with 15-inch girth would weigh around 5.63 pounds. The difference between 25-inch and 28-inch trout surprisingly matters when dealing with weight.
Rainbow trout usually live 4 to 6 years in the wild, although some reach up to 11 years. They eat meat, feeding on insects, crustaceans, fish eggs, minnows and other little fish.
