How Much Paint Should I Buy?

Before you begin painting your home’s interior walls, ceiling, woodwork, doors, or windows, you need to estimate the amount of paint you’ll use. Estimates require specific calculations for each surface you want to paint.

To estimate the amount of paint you need to cover the walls of a room, add together the length of all the walls and then multiply the number by the room’s height, from floor to ceiling. The number you get is the room’s square footage. Is that math class coming back to you now?

You have to determine how much of that square footage is paintable surface area. Because you use a different paint on the doors and windows, subtract those areas from the room total. No sweat, subtract 20 square feet for each door and 15 square feet for each average-sized window in the room. You end up with a number close to the actual wall area you have to cover with paint.

You can expect 1 gallon of paint to cover about 350 square feet. You need slightly more if the walls are unpainted drywall, absorbing more of the paint. It would help if you also considered whether to paint more than one coat. If you’re painting walls that are unfinished, heavily patched, or dark in color, plan on applying two coats of paint.

Professionals often add a color tint to the white primer when painting a dark color. Tints for both latex and alkyd paints are available at most paint stores. For best results, choose a tint shade closest to the top coat color.

Now for the clincher of the math problem. Divide the paintable wall area by 350 (the square-foot coverage in each gallon can) to find the number of gallons of paint you need for the walls. You can round uneven numbers; if the remainder is less than 0.5, order a couple of quarts of wall paint to go with the gallons; if the remainder is more than 0.5, order an extra gallon. Of course, buying in bulk is usually more economical, so you may discover that 3 quarts of paint cost as much as a gallon.