Our original fish weight estimator was based on measurements of length, girth, and weight of multiple fish species. We concluded that the best overall formula for estimating fish weight is:
weight (lbs) = length (inches from nose to fork of tail) x girth (inches) x girth (inches) / 690
The 690 divisor was a surprise to many people because it is so different from the well-known "traditional" and Sturdies formulas (which use divisors of 800 and 750 respectively). However, the Fly Fishing Research 690 formula is based on hard data, which shows clearly that higher divisors like 800 and 750 significantly underestimate fish weight on average (see our article in Fly Fisherman Magazine in 2008).
This section of our website reports the results of an in-depth and extended analysis for steelhead in particular. It is not based on hearsay or opinion, but rather on hard data of weight, length, girth, and gender of 115 of actual steelhead from multiple rivers in the Pacific Northwest. Our conclusions is as follows:
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