Quick estimate mode — for custom opening sizes, multiple wall types and material quantities:
Full calculator →
Quick Opening Calculator
Subtract windows and doors from your wall area to get the net area for paint or wallpaper.
Your Wall
All walls combined: perimeter × ceiling height.
Windows
Doors
Result
Net wall area
–
m²
Use this net area when buying paint, wallpaper or tiles.
Need different sizes per opening?
Full calculator lets you add each window and door individually with custom dimensions.
How to calculate net wall area
The formula
Net area = total wall area − (windows × w × h) − (doors × w × h).
How do I measure total wall area?
Measure the room perimeter (add all four wall lengths) and multiply by ceiling height. For a 4×5 m room with 2.4 m ceilings: (4+5+4+5) × 2.4 = 43.2 m².
Should I subtract all openings?
For paint — most painters skip subtracting small windows as the extra cost is minimal and it avoids running short. For wallpaper — always subtract openings since rolls are expensive and you cut to size anyway.
Pro tip: If windows and doors vary in size, measure each one separately and add the areas together before subtracting from the total wall area.