How to Measure a Fish
Size limits are generally based on the total length of a fish. The total length of a fish is the maximum length with the mouth closed and the tail pinched together measured from the snout to the tip of the tail. The best way to obtain this straight line measurement is to push the fish’s snout against a vertical surface with the mouth closed and with the fish lying along a tape measure and then pinch the tail fin closed to determine the total length.
Fork length refers to the length from the snout of a fish to the end of the middle caudal fin rays. This is the measurement for determining the legal size of a shark.
The girth of a fish is best measured with a fabric ruler. Measuring the girth is helpful in trying to determine if you have a possible record fish, which is determined by total weight. By using the total length and girth of a fish in inches you can get a rough estimate of the weight in pounds with this formula:
((Girth in inches x Girth in inches) x Length in inches) / 800 = Approximate weight in pounds