Estimate how many gallons of paint you need. Enter your wall measurements, coats, and openings, we subtract the doors and windows for you.
Estimates for planning only. Always confirm measurements and order a little extra for waste and cuts.
One gallon of paint covers roughly 350 square feet in a single coat. This calculator measures your walls, subtracts doors and windows, multiplies by your number of coats, and tells you how many gallons to buy.
We start from the paintable wall area, subtract openings, then multiply by coats:
Wall area = perimeter × ceiling heightPaintable = wall area − (doors × 21) − (windows × 15)Gallons = (paintable × coats) ÷ 350 (rounded up)
We use 21 sq ft for an average door and 15 sq ft for an average window.
Two coats is the standard for a durable, even finish and is what we assume by default. You can sometimes get away with one coat when repainting a similar color over a good existing surface. Plan on two to three coats when going from dark to light, covering stains, or painting fresh drywall (which also needs primer).
Six inputs, one formula. Wall area is your total wall length, the perimeter, times the wall height. The calculator subtracts openings using fixed averages: 21 square feet for each door and 15 square feet for each window. What is left is multiplied by your coat count, divided by 350 square feet per gallon, then rounded up to the next whole gallon. Enter an optional price per gallon and it multiplies that by the gallon count. The result rows show the paintable area and the coated area, so the raw numbers behind the rounding stay visible.
That 350 figure is the conservative end of typical manufacturer can-label guidance, which commonly states roughly 350 to 400 square feet per gallon for one coat on a smooth, primed surface. The 21 and 15 square foot openings are averages, not your actual doors and windows. Rough, porous, or textured walls absorb more and run closer to 300 square feet per gallon, so on that kind of surface the estimate reads light. Two coats is the default because two is the standard for an even finish.
What it does not do: it sizes wall paint only. Primer is its own coat and is not added for you. There is no allowance for waste, cutting in, or a spare can for touch-ups, and there is no labor in the number at all. The optional cost line is materials at the price you typed, nothing more. This is one of more than 50 free tools published at kellywm.com/tools, no email wall, and like the rest of them it runs in your browser and stores nothing.
Because paint is sold in whole containers. If the math lands at 2.2 gallons you are buying three, and the extra is worth having, since touch-ups years later match best when they come from the same batch. The rows under the result show the unrounded paintable and coated square footage, so if you are buying five-gallon buckets you can work from those figures instead.
No to all three. It covers wall surface only. If you are priming bare drywall or making a big color change, treat primer as an extra coat and run the numbers again with the coat count raised. Ceilings, trim, and doors usually take a different paint and sheen and should be calculated separately. Labor is never included, and the optional cost figure is gallons times the price per gallon you entered.