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  • Writer's pictureNew Wave Fishing Academy

Weight Estimate Chart Accuracy

Updated: Dec 16, 2023

If you fish you're always going to remember your personal best catch! Whether its by length or weight this becomes your goal to break on every outing in the future. To some only length matters, and to others only weight. Our opinion is that the true measure of how "big" a fish is or what is most impressive about the catch comes down to the weight. But, there is a lot of controversy around weighing fish as the methods for doing so can put a lot of stress on the fish especially for larger species. To avoid this some use weight estimate charts to determine the size of their catch. We will be perfectly honest in our opinion that these are terribly inaccurate and tend to overestimate weights! To us there is no point even trying to guess at the weight or estimate it as there are too many variables to consider which have an impact; what is the girth, where do you measure the girth, is it consistent or oblong shaped, is their belly full or empty, what size range was the formula built to, what forage have the fish been feeding on, are my measurements even accurate, the list goes on.

Our advice, don't claim a weight unless you put it on a scale or be ready to be challenged for claiming something that is unlikely. If you do need or want to weigh a big fish use a bag or keep the fish in the net while weighing to ensure the whole body is fully supported. Just be sure to tare the scale accordingly.

Big Georgian Bay Northern Pike
43" - 18 Lbs Northern Pike From Georgian Bay

Most weight estimate charts are based on three variables; species, length, and girth. However, ones which don't include girth are even less accurate as more assumptions are made. The general formula used for estimating fish weights is Length* Girth^2 / A where "A" is value specific to each species but this will also vary in each body of water. From this you can see the girth adds to most variability to the estimate as it is the dominate factor in the equation. Depending on the type of species measuring and the individual fish shape you may get drastically different measurements for girth depending where you take the measurement and thus a big weight range. In addition if length measurements are not completed properly the length can be skewed by a few inches. Length measurements should always be taken with the fish on top of the tape not tape on top of the fish as this method would induce error due to the curvature caused by the girth of the fish!

Biggest Georgian Bay Northern Pike
45.25" - 20.0 Lbs Northern Pike From Georgian Bay

Let's take for example a pike of 42" length and girth of 18 or 20". This is a reasonable range to expect someone to get if they take 2 measurements on the same fish from different locations quickly. Given the coefficient "A" equal to 900 and using the formula and rounding to nearest 0.25 lbs we would get weight estimates of 15.00 & 18.75 lbs. Thats a pretty big range for such a small difference in girth measurement which could depend solely on where you measured on the fish, if you went under or over fins, and even just how tight the tape was! Now lets look at if the 42" length is actually a 40" fish measured incorrectly. Using the formula we would get weight estimates of roughly 14.50 & 17.75 lbs. Looking at the two extremes this gives a potential range of 4.25 lbs just from measurement variability let alone if the fish had a full or empty stomach and other factors impacting its weight.

Monster Georgian Bay Northern Pike
42.5" - 20.50 Lbs Northern Pike From Georgian Bay

In reality the difference between a 14.50 and 18.75 lb fish is huge. If you were to hold both one after the other there is no comparison. An 18.75 lb fish is pushing fish of a lifetime status for just about anybody while the 14.50 lb is just another nice fish. If your personal best is something you care about knowing or trying to best it is likely to be beaten by a small margin at a time; we are talking a few ounces or 0.5" not a few pounds. On Georgian Bay we have caught dozens of pike in the 40 - 45" range and very few actually crack the 20 lbs mark while more people than we can count have told us they caught a 20 lber. We have boated healthy looking 45" pike that just hit 20.00 lbs as well as extra fat 41.5 or 42" pike that weigh 20-20.50 lbs. We have also caught healthy looking 42" fish weighing as little as 15 lbs. The differences in these fish while holding them are huge and extremely noticeable.

Huge Georgian Bay Northern Pike
42" - 17 Lbs Northern Pike From Georgian Bay

Online you may also see anglers trying to defend or ask about sizes based on the photo they took. In addition to the formula information above this is also not a reliable source as some photo angles or holds just simply make fish look bigger than they are! Proof of this is in the photos we have included in this article.

The resources below for fish weight estimating can be used to highlight the differences in weights various sources will come up with. Each estimation method is prone to error and at the end of the day are just estimates for your catch. The purpose here is not to show or claim they are incorrect but highlight that despite what you think or feel there is only one way to actually know how big the fish you caught is and that is to measure it!

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