Wall Area Calculator

Written byOleh Soloninupdated 5 October 2026

Room

Room length, m

Room width, m

Ceiling height, m

Windows

Window width, m

Window height, m

Doors

Door width, m

Door height, m

Advanced options

Other openings, m²

Arches, recesses or a balcony door, as an area.

Result

Area to decorate, m²42.2
Walls in full, m²45.9
Openings deducted, m²3.7
Perimeter, m17
Working
2 × (5 + 3.5) × 2.7 = 45.9 m² windows: 1 × 1.5 × 1.4 = 2.1 m² doors: 1 × 0.8 × 2 = 1.6 m² 45.9 − 3.7 = 42.2 m²
Floor, m²17.5
Floor and ceiling, m²35

Perimeter × height, minus windows and doors, with the working shown

Work out the wall area of a room for paint, wallpaper or tiles, from length and width or from walls of different lengths, with windows and doors taken out by number and size. Shows the working, perimeter, floor and ceiling.

Almost every decorating job starts with the wall area: it decides how much paint, wallpaper, plaster or tile to buy. The sum is simple — the room's perimeter times the ceiling height, less the windows and doors — but the details are easy to get wrong.

Here windows and doors go in by number and size rather than as a total you have to work out, and a room with walls of different lengths — L-shaped, with a bay or an alcove — is handled too. The full working appears under the answer so you can check it.

How to use

Choose the room shape: for a rectangle enter the length and width; for anything else list every wall length going round the room, separated by semicolons or spaces.
Enter the ceiling height, the number of windows and doors and their sizes. Put arches and recesses in as an area in the extra field.
Read the area to decorate and the Working line; floor and ceiling areas appear for a rectangular room.

Wall area formulas

The area of one wall is length × height. All the walls of a rectangular room come to perimeter × height, which is 2 × (length + width) × height. A window or door is width × height, and that is subtracted from the wall area.

If the walls differ in length, add them all up to get the perimeter and multiply by the height. Split a sloping ceiling or the wall under a staircase into a rectangle and a triangle, where the triangle is base × height ÷ 2.

Worked out with this calculator.
To find	Formula	Example
One wall	length × height	5 × 2.7 = 13.5 m²
All walls of a rectangular room	2 × (length + width) × height	2 × (5 + 3.5) × 2.7 = 45.9 m²
A window or door	width × height	1.5 × 1.4 = 2.1 m²
Walls to decorate	wall area − openings	45.9 − 2.1 − 1.6 = 42.2 m²
An irregular room	sum of wall lengths × height	(4 + 3.2 + 1.2 + 0.8 + 2.8 + 4) × 2.7 = 43.2 m²
A triangular section	base × height ÷ 2	3 × 1.2 ÷ 2 = 1.8 m²

Wall area for rooms of different sizes

Wall area grows with the perimeter, not the floor area: a 4 × 5 m room has 20 m² of floor but 48.6 m² of wall with a 2.7 m ceiling, more than twice as much. The figures below are before deducting openings.

Wall area = perimeter × height, without windows and doors.
Room	Floor area	Perimeter	Walls at 2.4 m	Walls at 2.7 m	Walls at 3 m
3 × 3 m	9 m²	12 m	28.8 m²	32.4 m²	36 m²
3 × 4 m	12 m²	14 m	33.6 m²	37.8 m²	42 m²
3.5 × 5 m	17.5 m²	17 m	40.8 m²	45.9 m²	51 m²
4 × 5 m	20 m²	18 m	43.2 m²	48.6 m²	54 m²
4 × 6 m	24 m²	20 m	48 m²	54 m²	60 m²
5 × 6 m	30 m²	22 m	52.8 m²	59.4 m²	66 m²

What to deduct for paint, wallpaper and plaster

For paint, wallpaper and tiles, take the windows and doors out or you will overbuy. For plaster, filler and primer, deduct the openings as well and add the reveals separately. Reveals are not the size of the opening: three reveals 0.2 m deep around a 1.5 × 1.4 m window come to (1.5 + 2 × 1.4) × 0.2 = 0.86 m², against 2.1 m² for the opening itself. Allow for waste separately.

For bathroom tiles, count only the height you are tiling: if the walls are tiled to 2 m, multiply the perimeter by 2 m rather than by the ceiling height.

What this calculator shows

The wall area to decorate and the full area before openings
How much was deducted for windows, doors and other openings
The working with your numbers, and each wall's area for an irregular room
Perimeter, floor and ceiling for a rectangular room

What to keep in mind

Walls are treated as upright rectangles of one height; add sloping or triangular sections separately.
Recesses, chimney breasts and boxing-in are not included; add or subtract their area by hand.
For a room given as wall lengths, the floor area is not calculated, because the lengths alone do not fix it.

FAQs

How do I calculate wall area with windows and doors?

Work out the area of all the walls, perimeter × height, then subtract the openings: a 1.5 × 1.4 m window is 2.1 m² and a 0.8 × 2 m door is 1.6 m². For a 5 × 3.5 m room with a 2.7 m ceiling that is 45.9 − 3.7 = 42.2 m².

How do I work out the area of one wall?

Multiply its length by its height in metres: a 5 m wall 2.7 m high is 13.5 m². Convert centimetres to metres first, so 350 cm becomes 3.5 m.

Should I deduct windows and doors?

Yes, for every finish. For plaster, primer and filler, add the reveals on top: 0.86 m² for a 1.5 × 1.4 m window with reveals 0.2 m deep.

How do I measure an L-shaped or irregular room?

Choose Walls of different lengths and list every wall going round the room, for example 4; 3.2; 1.2; 0.8; 2.8; 4 for an L shape. The calculator adds them into the perimeter and shows each wall's area.

Why is the wall area bigger than the floor area?

Because it depends on the perimeter and height. A 4 × 5 m room has 20 m² of floor, but its 18 m of wall at 2.7 m high adds up to 48.6 m².

Can two rooms with the same floor area need different amounts of paint?

Yes. A 3 × 6 m room and a 4.5 × 4 m room both have 18 m² of floor, but their perimeters are 18 m and 17 m, so at the same height the first has more wall to cover.

Worked example

A 5 × 3.5 m room

Input: 5 × 3.5 m, 2.7 m ceiling, a 1.5 × 1.4 m window, a 0.8 × 2 m door

Output: Perimeter 17 m, walls 45.9 m², 42.2 m² to decorate

Note: The openings take up 3.7 m². Wallpaper and paint are bought for the 42.2 m²; for plaster add the reveals to that figure rather than keeping the openings in.

Useful links

All tools in Building & Repair

Wall Area Calculator

Result

Related tools

Paint Calculator

Wallpaper Calculator

Tile Calculator

Useful links