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Since Musky fishing is generally Catch | Photo | Release you usually can't get an accurate weight for your fish. But you can estimate it based on the size of the fish. Google turns up many sites that have online calculators, but a lot of them don't show what formula they're using. There are several standard ways to calculate the weight of a Musky once you know the length and girth. Some require only the length and calculate the girth as a factor of the length using either 0.46 or 0.58 (it varies between sites) for that. Obviously you'll get a more accurate estimate if you have the actual girth measurement.

All of the sites that have details on how to measure your Musky for a weight estimate say that you want to use the "short length" which is the measurement from the tip of the lower jaw to the inner fork of the tail. This is different than the measurement that is taken to determine the size of your Musky, which is from the tip of the snout to the tip of the tail. The difference between the short and long lengths can be significant. This probably accounts for some of the differences between the formulas. As of this writing there doesn't appear to be any clear standard, not helped by the fact that most calculators don't say what their formula is based on, or sometimes even what formula they're using.

The age of the fish can also have a significant influence on the length to weigh ratio. If you look at the Utah Fish and Wildlife chart (near the bottom of the page) you can see that a 24 inch fish will weigh approximately 3.24 pounds. But a fish that's twice as long at 48 inches will weigh over 10 times as much at 32.76 pounds. Their source for that chart was the Indiana Division of Fish and Wildlife.

There are at least 7 different formulas that you can use to calculate the weight of your Musky. 14 if you consider that you could do it using the Short Length or the Long Length. More if you allow for variations in Girth/Form Factor. So the weight estimate isn't as simple as it sounds. For comparison purposes, after each formula we've included two weights caclulated by that formula, one for a 36x16 inch fish and one for a 44x20 inch fish.

• girth X girth X (length / 800) is what is considered the "standard" formula. (11.52 and 22.00)

• (girth-0.75) X (girth-0.75) X (length / 800) is a formula developed by Warren Wilkinson (or Larry Ramsell, different sites credit different authors) because he felt that the standard formula was resulting in weights that were too high. (10.47 and 20.38)

• 0.0000418 x ((length-cm X girth-cm)^1.441) which was developed by researchers Casselman and Crossman based on their measurements of 341 "trophy" muskellunge. (12.85 and 23.67)

• ((length-in X girth-in)/ 25) - 10 is the Crawford Formula resulting from a study of approximately 700 fish. (13.04 and 25.20)

• length X (girth X girth) / 900 is also used on one site. (10.24 and 19.56)

• (girth/800) X (length X girth) is a formula used by the Utah Division of Wildlife Resources, but they don't cite the source of the formula. (11.52 and 22.00)

• (length x length x length ÷ 2,800) is a formula developed by Doug Hannon, but he's a Bass Fisherman, so that formula may be skewed for Muskies. It's actually very close to the formula (length x length x length ÷ 2,700) that some sites use for Walleye calculations. Some test calculations show that this formula results in significantly higher weights. (16.66 and 30.42)

With one exception all the sites listed here show what calculations they're using, most have multiple calculators so you can get weights for different types of fish, one allows you to compare the results of 3 different formulas for the same fish, and one will let you pick the girth range of the fish for a more accurate estimate. You can use the online ones or you can pick out a formula and do your own calculations in the boat.

• csgnetwork.com doesn't list the formulas he uses, but he does give specifics that no other site does about obtaining the measurements. According to his site, the girth should be measured at the widest point, the length for purposes of an accurate calculation is the "short length" which is the measurement from the tip of the lower jaw to the inner fork of the tail. His calculator also allows for different body structures.

• esoxhunter.com has a form that allows you to enter one set of dimensions and get back the results from 5 different calculators.

• topofthefoodchain.ca will actually let you calculate the weight using three different formulas, one at a time.

• Ontarioanglerawards.com uses (Length) * (Girth * Girth) / 900.

• fishingreporters.com uses (length x length x length ÷ 3,500).

• fishinginfo.com also uses (length x length x length ÷ 3,500).

• jdunns.com uses length x (girth squared) ÷ 900. His form is set up to let you do three fish at once.

• mybaitshop.com doesn't list the details of their calculations, but they have a graphic that will give you an idea of how it all works. It also shows measuring to the inner fork of the tail.

• Outdoors Adventure Network has multiple calculators for different fish. And they specify using the "short length" measurement.

• www.fishdreams.com apparently uses the unnamed formula listed above.

• Utah Fish and Wildlife has a chart showing weights for different length Muskies.