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Estimating fish weight

Fishing Wisconsin

Fish are sometimes damaged when weighed. Using the appropriate formula for your species below, you can quickly calculate the "approximate" weight of your fish by using a ruler. You may also wish to download our trophy converter [PDF] in which we've done the math for you.

Please note when using the formulas:

  • length and girth are measured in inches,
  • girth is the distance around the body of the fish at its largest point, and
  • all answers are in pounds

To measure your fish:

Measuring a fish


A = length and B = girth


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

pike weight = (length x length x length) / 3,500

sunfish weight = (length x length x length) / 1,200

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

walleye weight = (length x length x length) / 2,700

For example, you catch a 16 inch walleye. Using the formula for walleye above: (16 x 16 x 16) / 2,700 = 1.5 pounds. Your walleye would weigh approximately 1.5 pounds.