How to Measure a Room for Paint

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How much paint do I buy for this room? There seems to be much confusion about calculating paint coverage when starting a painting project, but in reality, there doesn't need to be.

The accepted industry standard for paint coverage is 350 to 400 square feet per gallon of paint. However, this varies, because not all paint pigments (colors) are opaque. Yellows are quite transparent and will require several coats of paint to match the color chip. Reds and violet-blues, on the other hand, are extremely opaque. Whites are usually opaque, but coverage may vary slightly by the tint base of the white and the underlying color of the wall.

Quality of paint is another variable. Generally, architectural grades of paint have greater coverage capacity. Less expensive paint grades sacrifice opacity and brightness for price. Armed with this information as a basis, let's get started.

To break this down into easy-to-understand steps, there are several key points to remember. For rounding purposes, I'll use the coverage figure of 400 square foot per gallon. But you should remember to adjust that figure if you're using transparent pigmented paint. I recently painted my family room a bright marigold yellow and found that it took three coats.

What You'll Need

To measure for your paint coverage, you'll need the following supplies: a pen or pencil, paper, a tape measure and a calculator. It is also a good idea to know the shade and opaqueness of the paint you would like to use.

Measuring and Calculating

To calculate an interior room that is 10 feet by 12 feet with 8-foot-high walls, follow these equations.

There are two 10-by-8-foot walls, two 12-by-8-foot walls, and a 10-by-12-foot ceiling. The square footage you'll need to cover can be calculated this way 2(10x8) + 2(12x8) + 1(10x12). So, 160 + 192 + 120, which equals 472. That means there are 472 square feet of wall and ceiling to cover with paint. So, if a gallon of paint covers 400 square feet of wall space, then this room will consume 1 gallon, plus 1 quart for this room.

To be more particular, you can subtract the square footage of any windows, or of any doors you won't be painting. Single doors average 21 square feet, while windows average 16 square feet. Therefore, our room, with one single door and window, would have 37 square feet less (21+16=37) of wall area. French doors (double doors), of course, will average 42 square feet, and so forth for stacked or multiple windows. Always measure your own doors and windows, however, to account for any small differences.

Primer and Prep

Primer is needed for previously colored walls or walls that needed repair. Most primers will usually cover 200 to 300 square feet per gallon. Under-painting with primer adds another advantage in that it dries with a fine "tooth" to the paint surface, helping the final coat of paint adhere to the walls and ceiling better than it would without primer.

The typical homeowner will want to paint the trim (base boards, doors and windows) in a glossy paint, while most interior walls will be in a flat paint. The exceptions are kitchen and bathroom walls, which will usually be semi-gloss or gloss, simply for ease of maintenance.

Before painting, it is always a good practice to fill all the nail holes, and to scrub the walls, ceiling and trim with an aggressive cleaning solution to remove dirt, smoke and grease from all soon-to-be-painted surfaces. This ensures the best adhesion of the new paint. Always check the manufacturer's specifications for coverage area and surface preparation. Then, adjust your list of how much paint to buy.

Last Updated: July 22, 2011
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About Bill Washburn William "Bill" Washburn has a BA in advertising from the Art Center College of Design and has taught at the University of Southern California and Northrup University. Writing from a well-connected studio in the rural foothills of the west coast, he is a frequent speaker at local art associations and has published numerous articles discussing periods of art history and the fundamentals of drawing and painting. William is a master gardener who grows his own culinary herbs, organic heirloom vegetables and a variety of fruits. He writes frequently about his gardening experiences on his website Pioneer Dad. He is an accomplished advertising writer, fine art painter, and art director with more than 20 years' experience. 

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