Tools in this category
Area, coverage and offcuts
Quantities for finishing almost always follow the same sum: the area to cover, divided by what one unit of the product covers, plus an allowance for cutting. The paint calculator starts from the coverage printed on the tin, in square metres per litre per coat. The tile calculator adds a percentage for offcuts that depends on the laying pattern. The wallpaper calculator turns square metres into rolls.
Room area from its dimensions
Before any coverage rate, you need the area. For rectangular rooms and a ceiling height of 2.50 m used as an example, the table gives the floor area (the same as the ceiling), the perimeter, handy for skirting, and the gross area of the four walls before doors and windows are taken off.
| Room | Floor or ceiling | Perimeter | Walls (2.50 m high) |
|---|---|---|---|
| 3 × 3 m | 9 m² | 12 m | 30 m² |
| 3 × 4 m | 12 m² | 14 m | 35 m² |
| 4 × 4 m | 16 m² | 16 m | 40 m² |
| 4 × 5 m | 20 m² | 18 m | 45 m² |
| 5 × 6 m | 30 m² | 22 m | 55 m² |
Wall area is the perimeter multiplied by the height. For a different height, multiply the perimeter by yours: 14 m × 2.40 m = 33.6 m². The room area calculator does it with your measurements, takes off the openings and passes the result to the other calculators so you do not have to copy the figure.
Where to find the coverage
On the product’s technical data sheet, which manufacturers publish on their websites, or on the packaging. Coverage depends on the surface: new or porous plaster soaks up more paint than a wall that has already been painted. The calculators offer a starting value taken from a named data sheet and let you enter the one for your product. For tile adhesive, consumption depends on the notched trowel and the tile size, and the adhesive’s data sheet gives it for each combination.
Common mistakes
Taking off every opening for tiles or plasterboard: the cuts around them create waste, so only large openings come off and the allowance stays. Buying the exact number of boxes or rolls: a different production batch can be a slightly different shade, so buy everything at once with the same batch number. Forgetting the coats: paint is worked out per coat, and the tin says how many the manufacturer recommends.