"Estimating Weight"
  By: www.ThaiFishingGuide.com

The following formula is a well-proven method to very accurately estimate the weight of most game fish.
 

The measurements are all in inches and the final results in pounds, but this can then be transformed into kilograms.
 

The girth of the fish is measured on the greatest part and then squared.
 

This is then multiplied by the body length of the fish, measured as illustrated below.
 

This result is then divided by 800 to get the weight in pounds.

Example:
Girth is 3 feet 4 inches = 40 inches
Body length in 8 feet 4 inches = 100 inches

40 X 40 = 1600
1600 X 100 = 160000
160000 / 800 = 200 lbs.

To get the result in kilograms, the final number is then divided by 2.2.

Example:
200 / 2.2 = 88kg.