calcs.homes
calcs.homes
Enter your room dimensions, the openings to skip, and the number of coats, and this paint calculator gives the gallons to buy, the paintable area, and a cost estimate.
Estimate only — deep colors, textured walls, and a big color change can need an extra coat.
We add the four wall lengths, multiply by height for the gross wall area, and subtract a standard 21 sq ft per door and 15 sq ft per window. If you include the ceiling, its area is added. That paintable area is multiplied by the number of coats, then divided by the coverage on the can — usually about 350 sq ft per gallon — and rounded up to whole gallons.
Coverage falls on porous, patched, or heavily textured surfaces, and a big color change (dark over light, or the reverse) often needs a third coat or a tinted primer to look even. When your exact gallon figure lands just over a whole number — say 2.1 — buying quarts for the remainder can be cheaper than a third full gallon.
With 8-foot walls, one door, and two windows, about 1.9 gallons for two coats — so two gallons. Add roughly half a gallon per coat if you paint the ceiling.
Around 350–400 sq ft per coat on a smooth, primed wall. Rough stucco, bare drywall, or textured ceilings can drop that to 200–250.
For a small room the deduction is minor and adds safety margin if you skip it. For a room with large windows or several doors, subtracting keeps you from over-buying.