Fish Weight Chart and Formula

[mt_flyfisher]

As many of you know, a fish’s weight can be reasonably calculated using a mathematical formula that takes the length and girth of the fish into consideration. One such formula that is sometimes used for trout is: (length x girth x girth)/divided by 800. The divisor (800) can be increased or decreased if the fish you’re catching are heavier or lighter than normal, as might be the case for trout caught in a lake for example.

A number of years ago when I was doing a lot of steelhead fishing, and catching 30+ inch fish were pretty common, I made up this chart (approximately 3”x5”), had it laminated and carried it with me in my vest. I did get a few fish that were in the 36”-38” range as I recall, but never any that had girths as large as my chart went. 😞

Here’s another chart that I just copied from the internet that uses the same formula, and would cover many typical size trout caught around here. (It wouldn’t cover the sizes of brown trout that my doctor showed me pictures of yesterday that he caught in Iceland this past summer).

Feel free to make a copy of either of these charts (permission has been given for the Trout Unlimited chart above) or make your own, if you feel this would be of interest to you.

John

 

[Tigereye]

Would this be close for salmon? don't see why not.

 

[mt_flyfisher]

Would this be close for salmon? don't see why not.

It would be in the ballpark, but it would depend on where you were getting the salmon, and the species. The Chinook and Coho from the Salmon River at Pulaski might run a bit heavier on average than say do the trout in northern PA, so if you wanted to adjust the formula to improve its accuracy you could weigh a small sample of the fish where you’d be fishing and change the divisor (800) up or down as needed.

 

[dc410]

Thanks John. I’m wondering how close those charts would be for the local carp that I catch. It seems to me like it’s definitely in the ballpark. I often catch carp in the upper 20” range with a 20”+ girth and generally considered those type of fish to be in the 15-20 lb. range. If I pick up a carp with both hands to release it and my little fingers and thumbs don’t touch on either side the fish is generally well over 20” in girth. I used to have one of those “fish weigher things” but it only went up to 14 lbs. I bottomed it out on many occasions and finally busted it.

 

[mt_flyfisher]

Thanks John. I’m wondering how close those charts would be for the local carp that I catch. It seems to me like it’s definitely in the ballpark. I often catch carp in the upper 20” range with a 20”+ girth and generally considered those type of fish to be in the 15-20 lb. range. If I pick up a carp with both hands to release it and my little fingers and thumbs don’t touch on either side the fish is generally well over 20” in girth. I used to have one of those “fish weigher things” but it only went up to 14 lbs. I bottomed it out on many occasions and finally busted it.

I don’t know how well the chart and that formula would do for carp. You’d have to weigh and measure a sample of carp you catch and then compare them to the chart to determine if the chart is reasonably accurate or not.

I found a slightly different formula to estimate carp weights on the internet. That one says you start with a base weight of 6# for any carp that‘s up to 24” long. Then you add another 1# for every inch in length that the carp is over 24”, plus you add another 2# for every inch in girth that the carp is over 20”.

So, if you catch a carp that‘s 26” long, with a 24” girth, it would weigh approximately 16# (which is 6+2+8).

 

[Brown71]

Thanks for posting. They are surprisingly accurate.

 

[JimKennedy]

Thanks for posting. They are surprisingly accurate.

they are indeed. But they have a surgical procedure in Mexico, elective of course, that can address most concerns related to size.

My understanding is that it is cheaper than a four wheel drive pickup with v8 engine. Also, a lot of dudes who have the procedure are able to find regular work in a niche of the entertainment industry.

Also, a big fish, played, appreciated and released without being measured then has the opportunity to grow in the greatest habitat there is: the angler’s imagination. I personally have seen a trout grow from 12 inches to a solid four pounds over the course of a single afternoon following its capture and release.