Room area and wall area calculator
Enter the length, width and height of the room and how many doors and windows it has, and you get the floor area, the net wall area, the perimeter and the volume. The figures then travel to the paint or tile calculator in the link itself, so nothing has to be measured twice.
Openings come off the wall area: 1.9 m² per door and 1.5 m² per window as typical sizes, the same figures the paint calculator uses.
🔒 Worked out in your browser — nothing is sent to a server
Floor area
20 m²
and 50.6 m² of net wall
Breakdown
| Floor area | 20m² |
| Perimeter | 18m |
| Wall area | 54m² |
| Doors and windows deducted | − 3.4m² |
| Walls after deduction | 50.6m² |
| Room volume | 60m³ |
Carry these figures to
The figures travel inside the link itself, so you can see them, edit them and share them. Nothing is stored in your browser.
How it's calculated
Floor area is length times width, and it is the figure you need for tiles. The perimeter is the sum of the four sides, which is what you need for skirting or cornice.
Wall area is the perimeter multiplied by the height, which is the four walls laid flat. Doors and windows come off it, because they are neither painted nor tiled, and what is left is the net area, the figure the paint calculator wants.
Room volume is floor area times height, and it matters for ventilation and for understanding a cooling load. The tool does nothing beyond geometry: no prices, no materials, because it is a step on the way to the other calculators.
- Floor area = length × width
- Perimeter = 2 × (length + width)
- Wall area = perimeter × height
- Net wall area = wall area − (doors × 1.9 + windows × 1.5)
- Volume = floor area × height
Worked example
A 4 × 5 metre room with a 3 metre ceiling, one door and one window:
- Floor area: 4 × 5 = 20 m²
- Perimeter: 2 × (4 + 5) = 18 m
- Wall area: 18 × 3 = 54 m²
- Openings: 1.9 + 1.5 = 3.4 m²
- Net wall: 54 − 3.4 = 50.6 m², and the volume is 60 m³
Carry 50.6 m² to the paint calculator and 20 m² to the tile calculator. Both figures appear in the link, so you can save it or send it to whoever is doing the work.
FAQ
How do the figures reach the other calculators?
In the link itself. Pressing "Paint calculator" puts the number in the address, so the calculator opens with the area already filled in. You can see it in the address bar, edit it, and share the link. Nothing is stored in your browser or on a server.
What if the room is not rectangular?
Split it into rectangles, work each one out separately and add them up. For an L-shaped room it is enough to enter the largest rectangle and subtract the missing part by hand. Curved shapes need measuring on site.
Why are the door and window sizes fixed?
Because they are common sizes: an interior door of about 0.9 × 2.1 metres and a window of about 1.2 × 1.2. If your openings are very different, work out their real area and subtract it by hand before carrying the figure to the paint calculator.
Is the floor area the same as the ceiling area?
Yes in a room with a flat ceiling. A sloped or stepped false ceiling has a larger area and needs measuring separately. The paint calculator offers the ceiling as its own option, using the floor area.
Do I need the volume?
It helps with ventilation and with understanding a cooling load, since a taller room holds more air to cool. The AC size calculator takes the height directly, so there is no need to carry the volume across by hand.
Related tools
Sources
✓ Reviewed September 2026- Default opening sizes: an interior door of about 0.9 × 2.1 m (1.9 m²) and a window of about 1.2 × 1.2 m (1.5 m²), the same values the paint calculator uses so the two never disagree
- The calculation is pure geometry: no materials and no prices, and the figures travel to the other tools inside the link rather than in browser storage
Assumptions used
- A standard interior door leaf is about 0.9 x 2.1 m and a typical villa window about 1.2 x 1.2 m. Both are defaults the reader can override.