I found the following formulas in "Fish of Michigan" (by Dave Bosanko).  You may need a calculator for some of this (those of you who aren't good at mental math).

Bass weight = (length x length x girth) / 1,200

Pike weight = (length x lenght x lenght) / 3,500

Sunfish weight = (lenght x length x lenght) / 1,200

Trout weight = (length x girth x girth) / 800

Walleye weight = (length x length x lenght) / 2,500



I highly recomend this book and other books in this series (Fish of New York etc.) to any fishing fanatic (like me ).

I omly fish for fish with scales, but once in awhile I catch a catfish. They don't have scales.

Thanks fisherfanatic, do you (or anyone else) know if the bass weight calculation holds true for both smallmouth and largemouth?

Posted By t_mcginnis72 on 04 Dec 2010 09:01 AM
Thanks fisherfanatic, do you (or anyone else) know if the bass weight calculation holds true for both smallmouth and largemouth?

It should work for both Smallmouth and Largemouth Bass.

I caught a 6 pnd 14 oz bass that was weighed with two different scales. I used the formula for bass and the weight was 6 pnds 15 oz. WOW..Only 1 ounce off! I'd call that a pretty accurate method of estimating the weight. Thanks fisherfanatic, great info.

I found another calculation, lenght*length*length / 1600. Is this one fairly accurate as well?

I'm trying to guess the weight of a smallmouth I caught about 8 years back, I had no scale and little knowledge of fish weight. I did measure her and she was between 23 and 23.5 inches.

Oh yea, my little knowledge of fish weight meant I didnt get a girth measurement prior to letting her go, which is why I was wondering if the calculation without girth measurment is somewhat accurate.

Posted By t_mcginnis72 on 06 Dec 2010 08:48 AM
I found another calculation, lenght*length*length / 1600. Is this one fairly accurate as well?

I'm trying to guess the weight of a smallmouth I caught about 8 years back, I had no scale and little knowledge of fish weight. I did measure her and she was between 23 and 23.5 inches.

I don't think so...

There are different formulas.  I usually try to get a photo especially since many of us have cameras in our cell phones--learned the hard way that it is best to try it out before you miss that catch of a lifetime, especially tough if you practice catch and release.  I upgraded that formula to CPR--catch photograph and release.  In one of our NAFC club books:
THE BIG BOOK OF BASS there is a good formula that says:  Length X Length X Girth Divided by 1200 = Weight.  I have found it to be fairly close.  Of course, the best thing is a new set of scales.  I like the set made by Rapala.
Enjoy having to take the time to weigh one.  Uncle Tom

This web site won't do you much good in the field, unless you have a black berry or one of those other gadgets to access it, but I like the feature anyway. If you don't put in a girth I guess it uses an average # based on species and length.

http://www.bassresource.com/bassfis...lator.html