Wall and finish calculators
Four calculators for the surfaces of a room. Each one starts from the size of the room and ends with the number of cans, rolls, boxes or sheets to buy.
Last updated: September 28, 2026
In this section
- PaintHow much paint or primer for a room, one wall, a ceiling or doors and trim: litres or gallons and cans, with a table for 10×10, 12×12 and 12×14 ft rooms.
- WallpaperCalculate how many rolls of wallpaper to buy from the width and height of the walls, the roll size and the pattern repeat.
- TileHow many tiles and boxes for a floor, shower walls or a backsplash, with extra for diagonal and herringbone layouts, plus bags of grout and thinset.
- DrywallCalculate how many sheets of drywall or plasterboard a room needs from its size, the openings, the sheet size and an allowance for cuts.
Measuring walls
Measure the length of each wall along the floor and the height from floor to ceiling. For a rectangular room, the area of the four walls is twice the sum of length and width, multiplied by the height.
Doors and windows reduce the area for paint and drywall. For wallpaper and tile, small openings save little material, because the strips and tiles around them still have to be cut from full pieces.
Which calculator to use
- Paint: walls and ceilings of a rectangular room, with doors, windows and the number of coats.
- Wallpaper: rolls from the total width of the walls, the roll size and the pattern repeat.
- Tile: tiles and boxes for a wall or floor area, with grout joints and an allowance for cuts.
- Drywall: sheets of drywall or plasterboard for walls and, if you want, the ceiling.
If your room is not a rectangle, measure its floor area first.
Frequently asked questions
- Should I subtract doors and windows?
- For paint and drywall, yes: the calculators subtract the openings you enter. For wallpaper and tile, it is safer to measure as if small openings were not there, because the pieces around them are cut from full strips and tiles.
- How much extra should I add?
- The tile and drywall calculators start with an allowance of 10 percent, which you can change. Rooms with many corners and diagonal layouts need more. The paint and wallpaper calculators add no percentage; they round up to whole cans and whole rolls.
- Do the calculators cover primer, adhesive and grout?
- No. They calculate the main material only. The amount of primer, adhesive, grout and joint compound depends on the product, so use the coverage that is printed on its packaging.
- Is drywall the same as plasterboard?
- Yes. Drywall, plasterboard, gypsum board and wallboard are names for the same kind of sheet. Sheet sizes differ by country, so enter the size that your store sells.