Interior measurement
Wall Area Calculator
Estimate gross wall area, door and window deductions, and net paintable wall area before planning paint, wallpaper, or drywall quantities.
Paintable wall area result
- Room perimeter
- 44 ft
- Gross wall area
- 352 sq ft
- Door area
- 21 sq ft
- Window area
- 30 sq ft
- Total opening area
- 51 sq ft
- Metric net area
- 27.96 sq m
Visible assumptions
- All four walls are treated as a rectangular room perimeter by default.
- Doors, windows, and custom openings are subtracted from gross wall area.
- Net wall area cannot be less than 0.
Last reviewed: June 4, 2026
Calculate wall area
Use this wall area calculator when you need a surface estimate before painting, wallpapering, or planning non-structural wall materials. It starts with room perimeter and wall height, then subtracts common openings.
Wall area formula
Perimeter = 2 x (Length + Width)
Gross wall area = Perimeter x Wall height
Opening area = Door area + Window area + Custom opening area
Net wall area = Gross wall area - Opening area
Doors and windows deduction
Door and window deductions help avoid overstating paintable wall area. The default opening sizes are 3 ft by 7 ft for a door and 3 ft by 5 ft for a window, but you can edit those values to match the room.
Example calculation
A 12 ft by 10 ft room with 8 ft walls has a perimeter of 44 ft and a gross wall area of 352 sq ft. With one 3 ft by 7 ft door and two 3 ft by 5 ft windows, the total opening area is 51 sq ft, so the net paintable wall area is 301 sq ft.
How to measure walls
- Measure each room dimension wall to wall using one unit system.
- Measure wall height from floor to ceiling, not from baseboard to trim.
- Count doors and windows only when they reduce the surface you are estimating.
- Use custom opening area for pass-throughs, large built-ins, or other openings.
- For irregular rooms, calculate wall sections separately and add the results.
Common wall measuring mistakes
- Using floor area instead of wall area for paint or wallpaper planning.
- Forgetting wall height or using ceiling height from another room.
- Subtracting tiny openings too precisely while ignoring waste and product coverage.
- Mixing feet, inches, meters, and centimeters in the same estimate.
- Assuming an irregular room can be represented by one rectangle.
Wall area calculator FAQ
How do I calculate wall square footage?
For a rectangular room, add the wall lengths around the room to get perimeter, then multiply by wall height. That gives gross wall area before subtracting openings.
Should I subtract doors and windows?
Subtract doors, windows, and large openings when you are estimating paintable wall area. Very small openings may not change shopping quantities much, but keeping them visible helps explain the estimate.
Can I use this wall area for painting?
Yes. Net wall area is a useful starting point for paint estimates, but paint quantity also depends on coats, paint coverage, waste, surface texture, and whether the ceiling is included.
Can I use this wall area for wallpaper?
Wall area can help with early wallpaper planning, but roll size, pattern repeat, matching, and waste can change the number of rolls needed.
What if my room is not a rectangle?
Split the room into straight wall sections, calculate each wall or section separately, and add the areas together.