Wondering what your rainbow weighs? This rainbow trout length-to-weight chart gives a quick, scale-free estimate for trout in average condition.
Rainbow Trout length-to-weight chart
These values use weight (lb) = length cubed divided by 2,900 (length in inches) for a trout in good condition. Lake rainbows and steelhead carrying heavy girth often run heavier than the chart.
Why your fish may weigh more or less
A chart can only show an average, because two trout of the same length can differ in weight by 20% or more. A pre-spawn female, a fish fattened on a rich food supply, or simply a deep-bodied individual will all weigh more than the table suggests. Water temperature, season, and region matter too, which is why girth — the distance around the fish at its fattest point — is the single best predictor of true weight.
Get a weight tailored to your fish
For a number matched to your exact fish, measure both length and girth and drop them into our free fish weight calculator — it applies the proven length-and-girth formula and is usually accurate within 5–10%. New to measuring? Our guide on how to estimate a fish’s weight walks through it step by step.
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