Wall Area Calculator for Paint & Wallpaper
Enter the room size, wall height and any doors or windows. The wall area calculator gives the net wall area in m² and sq ft, the paintable surface that the paint and wallpaper calculators start from. The door and window rows start at common sizes (a 2 ft 8 in × 6 ft 8 in interior door and a 4 × 4 ft window), so change them to your own.
Wall area calculator
Bare numbers are meters; 190 mm works too.
Bare numbers are meters; 190 mm works too.
Bare numbers are meters; 190 mm works too.
- Wall length (perimeter)
- 15.60 m
- 51′ 2″
- Gross wall area
- 42.12 m²
- 453.4 sq ft
- Openings subtracted
- 3.09 m²
- 33.3 sq ft
- Net wall area
- 39.03 m²
- 420.1 sq ft
Net wall area: 39.03 m² (420.1 sq ft), from 42.12 m² (453.4 sq ft) of wall less 3.09 m² (33.3 sq ft) of openings.
How this was calculated
- Perimeter = 2 × (width + length); gross wall area = perimeter × wall height
- Openings = Σ width × height × count
- Net wall area = gross wall area − openings
- Perimeter = 2 × (4.20 m + 3.60 m) = 15.60 m
- Gross wall area = 15.60 m × 2.70 m = 42.12 m²
- Opening 1 = 0.81 m × 2.03 m × 1 = 1.65 m²
- Opening 2 = 1.20 m × 1.20 m × 1 = 1.44 m²
- Net wall area = 42.12 m² − 3.09 m² = 39.03 m²
How it works
Enter the room
Width and length inside the walls, or list each wall separately for non-rectangular rooms.
Enter the wall height
Floor to ceiling, or the height of the walls you are painting or papering.
Take off the openings
Add doors, windows and other openings. The calculator subtracts their area from the wall total.
Read the area
Gross wall area, the openings subtracted and the net area, in m² and sq ft.
The formula
Wall area = perimeter × height − Σ (opening width × opening height × count). For a rectangular room the perimeter is 2 × (width + length). Every opening is subtracted, and the result is the net area you need to cover with paint, wallpaper or plaster.
In feet: a 14 × 12 ft room with 9 ft walls has a perimeter of 52 ft, gross area of 468 sq ft. Take off one 3 × 7 ft door (21 sq ft) and one 4 × 4 ft window (16 sq ft): 431 sq ft net.
Doors, windows and other openings
Doors and windows are the main openings. Measure the frame size, not the brick opening: the wall area stops at the reveal. Include any other openings: fireplaces, ducts, built-in cupboards that stop at the wall. Measure each one and add it to the list.
Irregular rooms
Choose "Only the walls I list below" for L-shaped rooms, bay windows, chimney breasts and any shape that is not a rectangle. List each wall length and count. Walls that repeat (a pair of equal sides) share a count.
From wall area to paint and wallpaper
Paint: multiply the net area by the number of coats and divide by the coverage per litre or gallon on the can. With 2 coats, 431 sq ft of wall becomes 862 sq ft of painting. The paint calculator does this step for you, with a wastage allowance.
Wallpaper: a roll covers only the whole strips that fit in its length, not its full area. The wallpaper calculator divides the same net wall area by the area of those strips, with the pattern repeat and a wastage allowance.
Plastering, tiling or a skirting deduction?
Frequently asked questions
How do I calculate wall area from room dimensions?
Perimeter = 2 × (width + length); wall area = perimeter × height; subtract doors and windows. A 4.2 × 3.6 m room with 2.7 m walls has 42.12 m² of gross wall area.
Do I subtract the door frame or the brick opening?
Use the door or window frame size. The wall area stops at the reveal, the part you see when the door or window is open.
What about bay windows and chimney breasts?
List each wall separately. Both add wall area. A chimney breast adds its two sides (2 × depth × height); its front face replaces the wall behind it. List the front and both sides as separate walls, and measure each face of a bay.
How accurate does the wall area need to be?
Accurate enough to buy the right amount. A 5% wastage allowance covers the normal uncertainties. Measure to the nearest centimetre or inch.
Ready to plan your space?
It is free, runs in your browser and needs no account. Projects are saved privately on this device.