How to measure the square footage of a wall
Measure the wall's length and height in feet, multiply them, then subtract the area of each door and window. The formula is wall area = length × height - openings.
A wall 12 feet long and 8 feet high has a gross area of 12 × 8 = 96 square feet. Subtract a 21-square-foot standard door to get 75 square feet of paintable or tileable wall.
Measure each wall separately when lengths or ceiling heights differ. The room calculator finds floor area, while this wall calculation uses vertical surface area.
Wall area for a whole room
To find wall area for a whole room, add the length of all walls to get the perimeter, multiply the perimeter by the ceiling height, then subtract doors and windows. The formula is room wall area = perimeter × ceiling height - openings.
A 12 × 12-foot room has a 48-foot perimeter. With an 8-foot ceiling, the walls have 48 × 8 = 384 square feet before openings.
After subtracting about 36 square feet for one door and one window, the room has about 348 square feet of wall. For finished floor area across the building, use the house calculator.
Subtracting doors and windows
Measure each opening's width and height, multiply them, and subtract the result from the gross wall area. A standard interior door is about 21 square feet because 3 feet × 7 feet = 21 square feet.
Window sizes vary, so measure each window instead of using one allowance for every opening. Add all door and window areas, then subtract that total once from the wall area.
Small outlets are often left in a paint estimate because normal paint waste covers them. For tile and backsplashes, subtract larger windows and other areas that will not receive tile.
Using wall area for paint and tile
One gallon of paint covers about 350 to 400 square feet for one coat. Divide the paintable wall area by the coverage listed on the can, then multiply by the number of coats. Use the paint calculator for a full estimate.
A wall area of 75 square feet (ft²) equals 7.0 square meters (m²) and 8.3 square yards (yd²).
Use the square yards calculator for any area.
For wall tile or a backsplash, divide the tileable wall area by one tile's area, then add the waste allowance required by the layout. Use the tile calculator to estimate tile quantities.
A 348-square-foot room-wall area needs about 0.9 to 1.0 gallon per coat based on coverage of 350 to 400 square feet per gallon. Round up to the package size sold and account for the planned number of coats.
Wall square footage calculator summary
The Wall Square Footage Calculator finds paintable or tileable area with wall area = length × height - openings. For a whole room, multiply the perimeter by the ceiling height, then subtract doors and windows.
A 12-by-8-foot wall is 96 square feet before openings and 75 square feet after a standard 21-square-foot door. A 12 × 12-foot room with 8-foot ceilings has 384 square feet of wall before openings and about 348 square feet after one door and one window.