Paint Calculator
Enter your wall's perimeter and height, plus door and window counts, to get real gallons -- not just a raw area number.
Paint needed
2 gallons
Wall area
269 sq ft
Primer
--
At the defaults above (40 ft perimeter, 8 ft ceiling, 1 door, 2 windows, 2 coats) that's 269 sq ft of wall and 2 gallons of paint.
How it's calculated
The calculator starts from perimeter times height, subtracts the standard door and window opening sizes, multiplies by the number of coats, and divides by the coverage rate per gallon -- rounded up, since a gallon can't be bought as a fraction and running short mid-wall means a visible touch-up line once the new batch is mixed.
Keep going
- Painting new construction or a repair? The drywall calculator sizes the sheets, tape, and mud that go up before any paint does. Drywall Calculator
- Covering the same wall in wallpaper instead of paint? This calculator uses the same wall-area math to size rolls instead of gallons. Wallpaper Calculator
Frequently Asked Questions
Why does this subtract a fixed area for doors and windows?
Paint doesn't go on an opening, so a door (~21 sq ft) and a window (~15 sq ft) are subtracted from the raw perimeter-times-height area -- both are standard estimating defaults used by most paint retailers' own calculators, based on typical door and window opening sizes.
Why does this use 350 sq ft per gallon instead of 400?
Manufacturers commonly publish a 350-400 sq ft per gallon range per coat. This calculator defaults to the low end of that range since real coverage over textured, porous, or previously unpainted drywall often falls short of the manufacturer's best-case number -- you can raise it if your surface is smooth and already primed.
Do I need a separate primer coat?
Primer is recommended over new drywall, bare wood, a stain, or a big color change (especially dark to light). If you're recoating an already-painted wall in a similar color, primer is often skippable -- toggle it on only when it applies to your job.
Should I use one coat or two?
Two coats is the standard recommendation for a durable, even finish and is this calculator's default. One coat can work for a very close color match on a wall already in good condition, but it's more likely to show roller marks or patchy coverage.
Does the ceiling need its own paint?
Yes if you're painting it -- ceilings are typically a different, flatter paint sheen and are usually done in one coat, which is why the ceiling option here adds its own area rather than reusing the wall's coat count.