Wall Square Footage Calculator

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.

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.

Most homeowners under-deduct openings and over-buy paint. The standard rule of thumb is a door = 21 sq ft and a window = 15 sq ft, but real-world dimensions vary considerably.

Standard door sizes: interior passage 30×80 (16.7 sq ft), interior bedroom 32×80 (17.8 sq ft), interior bath 28×80 (15.6 sq ft), exterior entry 36×80 (20 sq ft), patio sliding 60×80 (33.3 sq ft), French double 60×80 (33.3 sq ft).

Standard window sizes: small bathroom 24×24 (4 sq ft), bedroom 36×48 (12 sq ft), large bedroom 36×60 (15 sq ft), picture window 60×48 (20 sq ft), sliding patio 72×48 (24 sq ft).

For a typical 12 × 14 ft room with 8 ft ceilings, 1 standard door, and 2 standard bedroom windows: gross wall area = 416 sq ft, minus 17.8 (door) + 24 (2 windows) = 374.2 sq ft of net paintable area.

Wallpaper isn't sold by square footage — it's sold by the roll, and rolls don't map to a clean number of square feet because pattern repeat creates waste. Knowing the difference saves real money.

A standard US single roll covers about 35 sq ft, but practical coverage (after pattern matching) is 27 sq ft. European rolls are larger (56 sq ft, 50 sq ft practical). Always use practical coverage in your calculation, not the rated coverage on the bolt.

Worked example: 374 sq ft of paintable wall area. With US rolls at 27 sq ft practical coverage: 374 ÷ 27 = 13.9 rolls. Round up to 14. With European rolls at 50 sq ft: 374 ÷ 50 = 7.5 rolls. Round up to 8.

Large pattern repeats (anything over 18 inches) need 20-25% more wallpaper than this calculation. Solid colors or small repeats are fine at the standard rate.

Wall square footage drives several other materials beyond just paint.

Drywall sheets: 4×8 sheets = 32 sq ft, 4×12 = 48 sq ft. For 416 sq ft of wall: 416 ÷ 32 = 13 sheets of 4×8, or 416 ÷ 48 = 8.7 sheets of 4×12. Always order 10% extra for cuts. Don't subtract for doors and windows when ordering drywall — you'll need full sheets to cut the openings out of.

Wainscoting (typical 36-inch height): use perimeter × 3 ft instead of perimeter × full ceiling height. For a 52 ft perimeter: 52 × 3 = 156 sq ft of wainscoting, plus the upper 5 ft of wall (52 × 5 = 260 sq ft) painted normally.

Acoustic / soundproofing panels: typically sold in 24×48 inch panels (8 sq ft each). For a 416 sq ft wall: 52 panels.