Wall Square Footage Calculator
Measure wall area for paint, wallpaper, drywall, or wainscoting. Multiply length × ceiling height, then subtract any doors and windows.
Wall Area Calculator
How to calculate wall square footage
Add up the length of every wall in the room (the perimeter). Multiply that total by the ceiling height to get gross wall area.
A 12 ft × 14 ft room with 8 ft ceilings has a perimeter of 52 ft. Multiplied by 8 ft, that's 416 sq ft of gross wall area.
Then subtract openings: a standard door is roughly 21 sq ft (3×7), a standard window is around 15 sq ft (3×5). Subtract each opening from your gross to get net wall area for paint or wallpaper.
Paint coverage rules of thumb
One gallon of quality interior paint covers about 350 sq ft in one coat on smooth, primed drywall. Most projects need two coats for full hide, so a gallon really covers about 175 sq ft of finished wall.
Textured walls (orange peel, knockdown) drop coverage by 15–20%. Heavily textured surfaces or first-coat-on-bare-drywall can drop coverage by 30%. Always check the can label for the manufacturer's rated coverage on your specific product.
Pro tips
Skip ceiling-only doors
Don't subtract for very small openings like outlets and switches — they're negligible.
Add 5% for cuts and edges
Paint trim, edges, and touch-ups add up. A 5% paint waste factor protects your project.
Wallpaper needs more
Wallpaper has pattern repeat waste — add 15–20%, especially for large repeats.
Buy paint by the gallon
Even if you need 2.3 gallons, buy 3. Color matching from a fresh batch is hard.