Formulas containing length as well as girth are often most accurate for estimating weight, because the fatness or plumpness of the fish is accounted for. If only length is available, the most accurate weights often are estimated from length-weight relationships for specific waters or regions. For instance, in some waters fish might be relatively “skinny,” and the weight estimate might be overinflated if based on a formula created from data on a water body where fish are “fat” or even “normal.” That’s why adding girth to the formula can help with accuracy. Formula’s containing girth, however, also may not be as accurate as we’d like, because of inherent differences in the shape of fish and finding the right adjustment factor (or “shape” factor) to use in the formula. And it’s important to measure girth carefully, and at the fish’s fattest point, as girth estimates affect weight estimates powerfully.

We have seen a bunch of charts that convert walleye or pike from their length to their weight.  They are all pretty similar, but of course a fish can also vary by the girth of the body so a 36 inch pike might be a couple more or a couple less pounds.  These lengths and weights in the conversion chart below are based on averages that we have found.  For example, the Saskatchewan Department of the Environment encourages the use of “weigh your fish with a ruler”.  It’s quicker and easier on a fish to just measure it rather than the extra handling and extra time out of water it takes to hook on a scale.

A 30 inch walleye averages 16 to 25 years old.  Growth rates largely depend on habitat quality and forage abundance.  After reaching maturity around year three, walleye grow between 0.5 and 1 inch per year.  Walleye also grow slower in northern latitudes where colder climates decrease their metabolism.  This results in 30 inch walleye that are older than average. 

 How To Determining The Age Of Walleye

In healthy walleye populations, males typically live for 15-20 years.  Female walleye out live males by 5-10 years and average a maximum life span of 24 years.  The oldest walleye on record was shown to be nearly 30 years old. 

To accurately measure the age of a fish, scientist use the otolith bone, which is the inner ear bone.  Much like aging a tree by counting rings in the wood, the otolith contains growth rings too.  They cut out the bone and crack it in half.  It’s then charred over a flame and viewed under a microscope to count the rings, which correspond to the walleye’s age.

You can also determine the age of walleye, yellow perch and sauger yourself.  Growth rings similar to the otolith bone also occur on the gill plat or operculum flap. 

Male And Female Walleye Growth Rates

Beneath the water’s surface competition is fierce and size matters.  For walleye, that means egg-bearing females need to grow faster and bigger than males.  In just about every walleye lake, males peak out at 12-15 years old and reach 24-26 inches in length.  

Females, on the other hand, often grow to 25 inches in half the time.  By 16 years, quality lakes produce giant, 30 inch female walleye.

How Much Does A 30 Inch Walleye Weigh

We anglers like to know how much a fish weighs.  It’s how you track a new “personal best” and gives you bragging rights among friends.  However, not everyone has a scale, nor is it always easy to weigh fish and release them safely back into the water.

On average, a 30 inch walleye weighs 10 to 12 pounds.  Of course, this can vary. Some fish are long and skinny while others may be plumped up with eggs during the spawn.   

Most of the time you can accurately estimate the weight of a fish from the length alone.  Add in a girth measurement and you can really dial in the accuracy of a walleye’s weight.  The girth helps to account for fish with larger bellies and should be factored in if you catch a spawning female.  

How Big Do Walleye Get

While a 30 inch walleye is big, they do get even bigger.  The world record walleye caught by Mabry Harper in 1960 was supposedly 41 inches long and weighed in at 25 pounds.  It’s reasonable to assume that a walleye that size is well over 20-25 years old.

Fewer than one percent of walleye exceed 30 inches.  You should definitely count your self lucky if you catch one.  However, water bodies with ideal habitat can consistently produce trophy walleye.  Places like Lake of the Woods, Lake Winnipeg and Lake Erie pump out 30 inch walleye more often.

Super-Thick Walleye.

Common example might be Lake Winnipeg greenbacks. Head looks awkwardly small compared to the body, the belly-fat rolls over your fingers, even the tail is thick/meaty/carries weight.

Formula: (length x girth x girth) / 750 = weight

Here’s an example from personal experience that was verified on a scale:

(28.75″ x 17″ x 17″) / 750 = 11.078 lbs

Average-Looking Walleye.

Fish is overall proportional and healthy. Has an average looking thickness compared to its length and head size. Gut isn’t belly floppin’ over your fingers, but it’s not skinny.

Formula: (length x girth x girth) / 800 = weight

Example from personal experience:

(30″ x 16.5″ x 16.5″) / 800 = 10.209 lbs

Walleye Weight Formula

The formula to calculate the weight for a Walleye that is 20 inches long and has a girth of 12 inches is as follows. Walleye have a shape factor of 750.

WEIGHT = LENGTH x GIRTH2 / SHAPE FACTOR

WEIGHT= 20 x (122) / 750
WEIGHT= 20 x 144 / 750
WEIGHT= 2880 / 750
WEIGHT = 3.84 pounds (This would be a very fat Walleye)

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