How the wall area calculator works
Walls form a band around the room. Laid out flat, they are one long rectangle as long as the perimeter and as tall as the walls. Subtracting the openings you will not cover gives the net area.
The chart splits the gross area into what you will cover and what the openings remove, and the diagram unfolds the four walls to scale.
Formula and assumptions
- L, W
- room length and width
- H
- wall height
- openings
- total area of doors, windows, and built-ins
Assumptions and limits
- All four walls share one height. Calculate split-level or sloped walls separately.
- The ceiling is not included; it is shown separately for reference.
Worked example
A 12 × 10 ft room, 8 ft walls, with 20 sq ft of doors and windows.
- Perimeter = 2 × (12 + 10) = 44 ft.
- Gross = 44 × 8 = 352 sq ft.
- Net = 352 − 20 = 332 sq ft.
These are the calculator’s default values, so the live result above matches this example until you change an input.
How to measure correctly
- Measure each wall at floor level and add them for rooms that are not rectangular.
- Measure each door and window: width × height, then add them up.
- Measure wall height from floor to ceiling, not to the top of the baseboard.
- Leave out walls you are not covering, such as a tiled wall in a bathroom.
Wall Area Calculator FAQ
How do I calculate the square footage of a wall?
Multiply the wall’s width by its height. A 12 ft wall that is 8 ft tall is 96 sq ft. For a whole room, multiply the perimeter by the height.
How much should I subtract for a door or window?
Measure it. A door’s area is its width × height; add the windows the same way. Avoid fixed allowances when a room has unusually large or many openings.
Does wall area include the ceiling?
No. The result is the four walls. The ceiling area (length × width) is shown separately because it is usually painted with a different product.
Should I subtract openings for wallpaper?
Usually not. Wallpaper is counted in full-height drops, and a window rarely saves a whole drop. The wallpaper calculator handles this differently.
How do I handle a wall with a gable or slope?
Calculate the rectangular part here, then add the triangle on top: half of the wall width × the extra height at the peak.
Can I use wall area for drywall?
Yes. Net wall area divided by sheet area gives a starting sheet count. The drywall calculator adds an allowance and rounds to whole sheets.