Use our painting calculator to take the guesswork out of buying supplies. This free paint estimator tool is a great way to make sure you don't buy too much or too little product for your next paint project. Plus, you can use it to figure out your average paint job cost per square foot.


Ready to tackle a paint job? Don't get started until you've used our painting calculator to determine how much paint you'll need. After all, few things are worse than getting halfway through your project and realizing you're a few gallons short. 

To use the painting calculator, simply plug in your wall area, the number of doors and windows, the manufacturer's estimate, and the condition of your walls. You may need to adjust the results depending on the painting method you plan to use, any trim you're adding, or the quality of the paint.  

You can also use this tool as a paint cost estimator. Our paint calculator takes square feet into account, so you can estimate the total cost of the project based on cost per can, or determine the painting charge per square foot. 

Wall area sq.ft. Number of doors doors Number of small to medium-sized windows (10 to 14 square feet) small windows Number of large windows (up to 20 square feet) large windows Manufacturer's estimate of square feet covered by a gallon sq. ft./gal

Condition of wall surface (choose one)

  Poor (porous, and/or with patched areas)   Good (well covered with paint that has at least a slight gloss)

  Gallons of paint needed per coat gal./coat

Editor's Tip: Every effort has been made to ensure the accuracy of this calculation. But before purchasing materials for any project, please check amounts with your suppliers or contractors.

More Helpful Paint Estimator Tips

Interior Painting

Your interior painting estimate (and, ultimately, the interior painting cost per square foot for your project) can depend on more than just the size of your wall. Add-ons, special wall treatments, and more all influence the total amount of paint you'll need. The following tips will help you take these additional costs into account: 

  • Keep trimwork and moldings in mind when you visit the paint store. In an average room, painting the trim requires about 1/4 as much paint as the walls.
  • Special paint techniques, such as the ombre wall shown here, require different proportions and colors. Consult the treatment's how-to instructions for exact paint measurements. 
  • When you're buying paint, don't skimp. Often, premium paint covers in one coat, while bargain paint takes two. High-quality paint usually retains its luster, washability, and vibrancy longer than cheap paint. Also, by buying an adequate quantity at the start, you'll ensure that the tint is even throughout—otherwise, if you have to buy extra, the tint may be ever so slightly off, even with computerized paint mixing.
  • When painting over paint, if the new color is very different from the existing color—and especially if the new color is lighter—expect to apply two coats.

Exterior Painting

Just like interior painting, bonus features and unusual techniques can sway the results of our exterior painting estimate. The following tips will help you adjust for painting methods, project conditions, and extra features. 

  • Our exterior paint calculator's algorithm is for applying paint with a brush or a roller. If you use a sprayer, you'll need about 30 percent more paint.
  • The most important part of an exterior painting job is the prep work. You do NOT want to rush this step. Learn how to treat mildew, remove loose paint, fill cracks, and more with our guide to painting a home's exterior.  
  • If the existing surface is stained, or if it has patched areas, apply a coat of stain-sealing primer before applying the paint. Also, use primer if you will be applying latex paint and the existing paint is oil-based (or if you suspect that it might be oil-based). A good paint store will tint primer—at no extra cost—to approximate the color of the finish paint.
  • If you're just painting your home's exterior door, you'll likely only need a quart of primer and a quart of exterior paint. Learn how to paint an exterior door, here.


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