Estimating Interior Paint

By: Fix-It Club
Any room in the house can be enhanced with paint. But how much?
2009 HowStuffWorks

Estimatin­g the paint you'll need for a job is easy. Take a few minutes at home to measure the area to be painted. A gallon of paint will typically cover 450 square feet according to the manufacturer's calculations. It's safer to figure 400 square feet of cove­rage per gallon of paint. If you're buying 2 or more gallons of the same color, it's a good idea to mix them all together at home so color variations don't show up in the ­middle of a wall.

To determine the amount of paint required to cover a wall, multiply the height of the wall by its length, then divide by 400. This means a gallon of paint will cover a 10 X 15-foot room (two 10-foot walls and two 15-foot walls, 8 feet high) with one coat. Two coats will take 2 gallons.


However, there are other factors you should consider when calculating coverage.



Calculating Paint Coverage

Textured Walls

When a wall is textured or rough-troweled, it will require more paint than if it were a smooth wall. This is because the texture represents added surface to be covered, even though it does not contribute to the size of the area. Just how much more surface area there is depends on just how textured the surface is, but for medium-rough, porous, or previously unpainted walls, you can safely estimate 300 to 350 square feet of coverage from a gallon of paint.

Doors and Windows

Most walls have doors or windows or other areas that are not painted. If the nonpainted area is a single window or door, ignore it in your calculations. Two or three windows, a door and a window, multiple sliding doors, or a fireplace reduce the paint you'll need. By how much? Multiply the lengths by the widths of these nonpainted areas to get the total square footage that you can subtract from your overall surface figures, or you can subtract about 15 square feet for typical windows and 21 square feet for typical doors. (These figures also can be used to estimate the paint you'll need for each if you plan to use a different color or surface finish.) If you're painting the ceiling, figure its square foot area at width times length, too.


Speed Factor

Estimating the time you'll have to put in on any given paint project is less precise. Some people work faster than others, so there's no way to estimate individual differences in speed. On the average, you should be able to cover about 120 square feet of flat surface in about an hour. For bare wood or plaster, figure about 100 square feet. In a typical 12 X 15-foot room, you're likely to spend four or five hours on the job, including trim work, for the first coat. The second coat, if it's necessary, will go faster, but you'll have to wait for the first coat to dry, anywhere from 2 to 36 hours.


Lots More Information

Not what you're looking for? Try these helpful articles:

  • House Painting: Ready to tackle a house painting project? Gather helpful tips on both interior and exterior painting in this home improvement article.
  • House Painting Tools: Before taking on any painting project, make sure you have the tools you'll need to do the job well. This article will help.
  • Painting Interiors: Learn the essentials of painting walls, doors, and everything inside the house on this page.
  • Paint Rollers: Find out when a paint roller is the best tool for the job on this page.