Length-Weight Formulas to Estimate Fish Weights

Enter the fish's total length and girth in inches (see here for how to measure properly), into the yellow boxes, using decimals for fractions. The formula will convert the figures to millimeters and generate estimated weights. (If you have the measurements in millimeters, you can enter them in the pink boxes). Calculations are automatically completed when you click outside the box. The answer in the blue box is considered to be the most reliable for Florida bass, the answers in tan boxes are from commonly used alternative formulas. The primary estimate is derived from a rather complex formula, which is what Commission biologists use. The equation is:

Log (weight in grams)= -4.83 + 1.923 x Log (total length in millimeters) + 1.157 x Log (girth in millimeters). A 22" long bass with a girth of 15" weighs about 6.0 pounds using this formula.

(Note Internet Explorer 4.1 or higher may be needed to use this spreadsheet. It can be downloaded for free from here)

If you are unable to use the formula above because of your browser, some simpler equations are available:

A quick, though very rough, estimate of torpedo shaped fish like young bass can be obtained by using: Total Length (in inches)-squared, times girth (in inches) divided by 1200. A 22" long bass with a girth of 15" weighs about 6.1 pounds using this formula.

Another common option used for estimating bass weights is: Girth (in inches)-squared, times length (in inches) divided by 800. A 22" long bass with a girth of 15" weighs about 6.2 pounds using this formula.