How to Determine How Many Gallons of Paint an Exterior Needs

Measure the height of an exterior wall from the roof to the foundation.

Measure the four sides of the house or building. Add the four numbers, which will be the total width. For instance, if two sides of the home or building measure 16 feet and two sides measure 40 feet, the total of the four sides equals 112 feet.

Multiply the total width by the height to get the square footage. For instance, if the height is 8 feet, then 112 multiplied by 8 equals 896 square feet.

Subtract the square footage of windows and exterior doors from the total. Estimate each window as 15 square feet and each door as 20 square feet. Add the number of windows and multiply it by 15 and the number of doors by 20. Add these numbers together and subtract them from your total. If the number of windows equals 6, multiply it by 15 equaling 90, and three doors equals 60. Add the two numbers together for 150 square feet and subtract it from the 896 total equaling 746 square feet.

Divide the total square feet by 350 or the amount of coverage the paint can indicates. In this example, 746 square feet divided by 350 equals 2.13 gallons of paint. Double the estimate if applying two coats of paint.