Paint, Wallpaper & Drywall Calculators
Coverage is the whole game. A gallon of paint covers roughly 350–400 sq ft per coat, a roll of wallpaper covers a set width, and a 4×8 drywall sheet covers 32 sq ft. These calculators do the area math and add waste so you buy exactly what you need.
Paint: start with wall area, not room area
Buying paint by "rooms" is how you run out. Measure the actual wall surface: 2 × (length + width) × wall height, then subtract the doors (~21 sq ft each) and windows (~15 sq ft each) you won't paint. Divide by your paint's coverage — the 350–400 sq ft/gal range covers most flat and eggshell finishes — and multiply by the number of coats. One coat of primer plus two coats of finish is the standard for a repaint, so most rooms need 2–3 gallons for two coats. Always round up to whole gallons.
Wallpaper: pattern repeat changes the count
Wallpaper is sold by the roll or double roll, and each roll has a usable coverage that shrinks when the pattern needs matching. Measure the wall width × height, and use a calculator that factors in pattern repeat so you don't fall short mid-wall or buy a second roll for one strip.
Drywall: sheets, not feet
Drywall comes in 4×8 ft sheets (32 sq ft each; 4×12 = 48 sq ft). Divide your wall and ceiling area by the sheet size, then add roughly 10% for cutting around windows, doors and corners. Plan sheets so the long edge runs across studs, and account for seams.
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Related guides
Go deeper with our step-by-step guides on coverage, priming and measuring: