Estimate the weight of salmon or trout by length and girth

fish weight calculator

Fish'o'meter - a unique ready reckoner for estimating the weight of fish.

Releasing a brown trout

With many salmonid stocks diminishing in numbers, more and more anglers are now returning fish rather than keeping them. However, it is difficult to accurately weigh a fish which is still alive, so we developed an equation to calculate this as accurately as possible. Only two measurements are required, length (to the fork in the tail) and girth (measured immediately in front of the dorsal fin). Both measurements can be made quite easily using an ordinary measuring tape. Measure your fish in centimeters and then add your measurements in the boxes below. The formula is based on the measurements obtained from over 800 adult Atlantic salmon sampled during the summer of 1994. For most fish, this should give a weight which is within 5% of the actual weight. Although the formula was calculated using salmon, I have been informed that it is reasonably accurate for other salmonids such as trout. Formula was derived by Alastair Gowans B.Sc. CEng. and Andy Gowans Ph.D.

For comparison, weights are also estimated using formulae derived from NASCO and the Salmonid Council for Newfoundland and Labradors' data. We have also extrapolated a length-only equation based on our own existing data, so if you don't know the girth of your fish, fear not!

If you would like to more about the formula then e-mail me for details. My apologies if your browser doesn't support Javascript!

How long was your fish (in centimeters)?

What was the girth of your fish (in centimeters, not essential!)?

Using the available data sources, your fish weighed:



Our own data


Salmonid Council of Newfoundland and Labrador

Mean estimate

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Copyright 2007 Alastair Gowans AAPGAI and FFF Master and THCI, APGAI. All rights reserved.