Measure a boat for a cockpit cover by determining the width and length of the cockpit, typically in inches. Also, take the measurement of the circumference of the cockpit by using a helper to hold a string or flexible tape measure. For larger watercraft, also determine the height of any windshields and note upright poles.
Cockpit covers for larger boats generally attach with series of snaps or zippers affixed to the outer circumference of the upper boat hulls. Many types of watercraft feature bimini tops that require the covers to have predetermined cutouts to wrap around the upright frames.
The range of kayak cockpit cover sizes varies from approximately 15 to 22 inches in width by 28 to 38 inches in length, although different brands of kayaks sometimes have larger or smaller cockpits. Kayak cockpit covers, along with sprayskirts, are designed to fit snugly in the upper opening of the boat. The difference between the two is that the first blocks the opening, and the second has a center hole designed to cinch around the craft operator. Covers are made from a variety of materials, typically water resistant or waterproof. These include neoprene, nylon and plastic mesh. Some models of covers incorporate gear storage pockets.