When measuring a fish for a proper fit, make sure the fish is straight and flat. Measure from the center of the eye to the base of the tail where the scales stop and the fin rays begin (this is the portion of the fish carcass that the mannikin is going to replace.) Next, measure the girth at the thickest part of the fish. This is usually just in front of the spiny dorsal fin. When selecting your mannikin keep in mind you may order a form with a length measurement (center of eye to base of tail) a 1/2" shorter up to the actual length of the fish, but never longer than the fish. The girth measurement of the form should be approximately 1/2" smaller than the fish. Using a mannikin less than 1/2" smaller in girth will cause a slight gap where the incision was made. Example: if you have a bass that measures 16" in length and has a girth of 15", any mannikin that has a length from 15 1/2" to 16" and a girth of 14 1/2" to 14 7/8" should fit properly.