MetraNestFour walls, one height
For a rectangular room with a constant height, multiply the perimeter by the height. Measure length and width at the same level. If the room has a recess, a slope or different heights, divide the walls into sections and add their areas.
Subtract openings once only
A rectangular opening’s area is its width multiplied by its height. Add together the openings to exclude and enter the total. Use actual dimensions: a standard value may change the result, especially in a small room with large windows.
Choose what to measure
The net result covers the main wall faces. Reveals, niches and returns may add small areas that need separate measurement. The ceiling is not included in the walls: for a rectangular room, its area is length multiplied by width. No material allowance is added here.
Gross wall area = 2 × (length + width) × height. Net area = gross area − total opening area.
A bedroom with a door and a window
For a room measuring 4 × 3 m with a height of 2.50 m, the walls cover 35 m². A 0.90 × 2 m door and a 1 × 1.20 m window subtract 3 m². The net area is therefore 32 m². The ceiling adds 12 m² if it will also be treated.
Details to check
- Use the same unit for all dimensions.
- Keep openings on a separate line in your measurements.
- Transfer the net area to your chosen quantity calculator.
Frequently asked questions
Why is the wall area greater than the room’s floor area?
Floor area measures the floor. Wall area adds four vertical faces: they are two different measurements.
Can I subtract every opening for wallpaper?
Net area is a useful reference, but rolls are calculated by full strips. Offcuts around openings require a different approach.
Method and references · Editorial review: 25 October 2026
The geometric formulas are explained here. For a product, its packaging dimensions and coverage rate remain the reference inputs.