What should I expect for topside paint coverage?

For the best performance and appearance, topside paints generally specify a recommended number of coats. Most topside paints provide a few different numbers correlating to coverage.  

To more accurately determine how much paint is necessary to paint a boat, it's very important to measure the area to be painted properly. Always include any changes in sheer, bow flare, chines, or other structural shapes. As a general rule of thumb, buy a little more paint than you need because if you don't have enough, the surface will show poorly where you started and stopped.  

Yield/coverage: This number indicates how much area the product will cover in one coat, and is generally based on the container's size. For example, TotalBoat Wet Edge quart containers state that the coverage is approximately 80-100 sq. ft./quart. This means that when this paint is applied at the proper thickness, one should expect between 80-100 square feet of coverage for one coat.  

Application thickness: This is a very important factor that is sometimes overlooked. Paint manufacturers base this number on the wet film thickness (WFT) the paint should be to cure properly in the designated time frame, as well as to give the paint the best flow and self-leveling characteristics. When paint is applied thicker, it may lead to much longer cure times, drips and sagging, more dust in the paint job, or even hazy looking finishes. If the paint is applied thinner than the designated thickness, it's not always detrimental, but the paint may not have the desired flow, and it may need more coats to achieve the best color, finish, and performance.

Number of coats: Most paint manufacturers post the number of coats they recommend for their product based on application thickness of the paint, as well as how many coats it takes for the best color, finish, and UV protection. Certain colors may also require more coats.

Waste: When paints give a yield or coverage, it's very important to assume that some of the paint will go to waste. Even the most efficient painters will lose some paint in the brush or roller, paint tray, drips on the ground, or even dripping down the side of the can. More paint wasted, means less paint available for the project. Though it's hard to judge fairly the amount of paint that will go to waste, depending on application type, 10% is a conservative amount to assume will be wasted. If more rollers or brushes are used, the waste percentage may increase.

Thinners: Thinners do not add to a paint's coverage. They are specified for different application methods to help improve the flow and working characteristics. Always have the proper thinner necessary for the desired application method. Paint manufacturers will usually state a general percentage of thinner to use. 

Below is a general yield chart for air dry paints such as Interlux Brightside, TotalBoat Wet Edge, and Pettit EZ-Poxy. Be sure to calculate any waste and necessary thinners.