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Determining How Much Paint to Buy

Updated on May 1, 2015

When it comes to determining the amount of paint you need to buy for a project, there are a host of factors to take into consideration, including the size of the house, the kind of coating selected, the method of application, and the condition of the surfaces. For example, stucco and masonry wallscan require up to 50 percent more paint than smooth and flat walls. Many airless sprayers apply the equivalent of two traditional coats at a time, so you may need double the amount of paint than if using a brush or roller. To come up with an accurate estimate, you need to take into account all of the above and then measure the surface that is about to be painted.

How to Measure an Area to Determine Paint Quantity

Surface Area = Height x Width

To estimate the amount of paint you need to cover interior walls, determine the length of the wall or surface area and multiply by the height of the area to be painted in order to get the square footage. Once you've determined the square footage of your project, the next step is to determine how much of this space is not going to be painted and since different paints will presumably be used on windows and doors, you will need to add up the square footage and subtract it from your original total.

As a rule of thumb, experts suggest that you will need approximately one gallon of paint for every 350 square feet. If you are painting walls and the surface is unpainted drywall, you will need more product, because bare drywall will absorb more of the paint. It is also necessary to decide if you need more than one coat of paint. You normally need two coats if the surface is heavily patched, unfinished, or of a darker color than the new one. It should be noted that professionals often add a color tint to the white primer and you can purchase tints for alkyd or latex paints at most DIY and paint stores. DIYers may want to stick with choosing from the most popular interior paint colors and schemes, rather than mix their own paints or primers.

Calculating the Paint Needed for a Standard Room

Measure twice and paint once!

These examples are for a room that is 14′ x 15′ and has eight-foot ceilings with two windows and two doors. To find out how much paint you require for the ceiling, you have to multiply the length of the ceiling by its width (14′ x 15′ = 210′) and then divide by 350 (the amount of feet per gallon); the result is 0.6, which means that you need approximately 0.6 gallons of paint per coat.

To find out how much paint is needed for the walls, you have to calculate the length and width of each (14′ + 15′ + 14′ + 15′ = 58′) before multiplying this figure by eight (the height of the wall). This gives you (58 x 8 = 464 square feet). Instead of measuring the doors and windows individually, it is possible to use rough estimates and simply subtract 15 feet for each door and 20 feet for each window (15′ + 15′ + 20′ + 20′ = 80′). Now subtract this from the wall area (464′ - 80′ = 384′) and you have the total paintable area. Divide this by 350 (384/350 = 1.09) and you discover that you require an estimated 1.09 gallons of paint for each coat.

The above calculations may seem a bit tricky at first, but they are actually very simple. Just be sure to use a calculator and take into account the finished surface of the area being painted and you should be able to provide an accurate estimate for the amount of paint needed for the task. And as any good contractor will tell you, Measure twice; cut once. Or in this case, measure twice; paint once!

How to Paint a Ceiling Provided by Dunn-Edwards Paints


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