Why 690 for Steelhead

Individual-Fish Divisors

Individual Variability

Fat vs Thin

Girth Taper

Improved Weight Estimator

Buck vs Hen

Variability By River

Conical Fish Model

Data Sources

Steelhead Weight

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:

Please click on the following links to learn more about these sources of variability and how much difference they make: variability by individual, variability by gender, and variability by river.

Any such analysis is only as good as the data on which it is based.  Fly Fishing Research is fortunate to have acquired data from highly credible sources

If you have additional data that includes length, girth, weight, gender and river of actual steelhead, please send it to tom@flyfishingresearch.net. We will update our records and analyses from time to time and credit you for your contributions accordingly.