The Caddis Fly: Oregon Fly Fishing Blog

Tom Keelin, an engineering guru and fly fisherman, recently published a new, more accurate way to estimate the weight of fish. The article ran in the May 2008 issue of Fly Fisherman. The conventional formula: weight = length x girth (squared)/800 underestimates the true weight of steelhead, according to Keelin. The more accurate equation, based on collected data from 87 steelhead weighed on an IGFA certified scale, is: weight = lenthg x girth (squared)/690.  Keelin says using a denominator of 690 correctly estimates a steelhead’s weight within one pound, 80% of the time.

Keelin’s Website, FlyFishingResearch.net, features an article explaining how to calculate fish weight, as well as an online fish weight calculator.