Estimating Fish Weight

[MrBill]

Ever wondered how much your fish weighs and you don't have a scale. Here's a formula that works for both Tuna and Billfish.

Girth X Girth X Length Divided by 800.

Example: A tuna has a 48" girth and the length is 69." The girth is measured all around the fattest part (usually at the dorsal fin). The length is from the tip of the nose straight down the lateral line to the middle of the fork of the tail.
48 X 48 X 69 = 158,976. 158,976 divided by 800 = 198.72 pounds.

On a billfish, measure from the tip of the lower jaw to the middle of the fork.
And here's another way to measure Blue Marlin that's a bit simpler and sometimes more accurate. Simply take the measurement around the ankle of the fish just ahead of the tail. 12" will be a 200 pound fish, and for each extra inch, add 100 pounds. To make that magical "grander" mark, the ankle will be about 20 inches. This method only works for larger Marlin. (300+ pounds)

If your real lazy and don't know how to multiply and divide, go to this site and plug in the girth and length.Kona's Big Game Fish Weight Calculator

This sheet is worth printing and laminating in plastic. I always have one with me. Keep it in your boat or tackle box. It works for both Tuna and Billfish. http://www.fishkona.org/fishest.PDF

If you are confused about the girth and length, go to this site for visual info on Tuna, Billfish and sharks. Estimating Weight - Saltwater Fishing Techniques - Thai Fishing Guide



Mackerel, Redfish, Snook, Corbina, Croaker, drum, bluefish, snapper, grouper, seeabass, perch, pompano, sheepshead, rockfish, trout, barracuda, bonefish, wahoo, sturgeon, tuna, halibut, flounder, sole, etc., go to this site. Salt Water Fish Weight Calculator



For fresh water fish like Salmon, trout, herring, shad, pike, muskie, gar, walleye, splake, sunfish, bluegill, crappie, bass, striper, carp, catfish , etc., go to his site.
Fresh Water Fish Weight Calculator

[STx Fisherman]

Thanks for the post Mr. Bill.....pretty useful....

[Bret]

good info right there.. Now I need to go fishing.

[Gunsmoke]

Originally Posted by MrBill

And here's another way to measure Blue Marlin that's a bit simpler and sometimes more accurate. Simply take the measurement around the ankle of the fish just ahead of the tail. 12" will be a 200 pound fish, and for each extra inch, add 100 pounds. To make that magical "grander" mark, the ankle will be about 20 inches.

I saw a guy lose all his teeth trying to use that method. If you have the huevos to attempt that on a semi green marlin I suggest you keep a baseball catchers mask on board. A 500 pound or larger marlin will rearrange your face in a hurry. Imagine bending over the gunnel and using both hands to measure a green marlin's tail. Your face is fully exposed and a prime target. A pissed off big marlin just might send you to a plastic surgeon.

[STx Fisherman]

When you have a marlin that is possibly a grander.....what the heck do you do? I would like to release any blue marlin, (or any fish that I don't care to eat), that I catch...but if it's a big fish...I want to know the weight. I am not a billfish fisherman but after going to PV I started wondering about things like this. I would like to know the weight of my blue marlin if it is anything > 500 lbs. What do the "experts" do?......the measurement calculations?

[Ragman]

Txseadog created a spreadsheet -then reduced it down to a laminated, business card size- that estimates the weight of your tuna based on measurements.

I still carry it with me today. Maybe he can post it?

It's been very accurate for me.