Walls, ceiling & primer
How much paint a room needs: the walls from the room's size or one wall at a time, less doors and windows, times the coats, at the coverage printed on your tin. In litres or US gallons, with the tins to buy.
Paint to buy
34.55 m² of wall, 2 coats at 10 m²/L + 10% extra.
| Product | Needed | Tins (least left over) |
|---|---|---|
| Wall paint | 7.6 L (2.01 US gal) | 1 × 5 L + 3 × 1 L (0.4 L spare), or 1 × 10 L |
| Surface | Area |
|---|---|
| Walls | 37.5 m² (403.6 ft²) |
| Doors × 1 | − 1.51 m² (16.2 ft²) |
| Windows × 1 | − 1.44 m² (15.5 ft²) |
| Wall to paint | 34.55 m² (371.9 ft²) |
Coverage is for a smooth wall that has been painted before. New plaster, bare wood, rough or patched walls and big colour changes soak up more: a primer or mist coat first, or an extra coat.
Choose Whole room and enter the floor's length and width and the wall height; the calculator walks round all four walls. For a feature wall, a stairwell or an odd-shaped room, choose Wall by wall and add each wall's width and height (a sloping wall can be entered at its average height).
Count the doors and windows and give a typical size; the example uses a common UK internal door (762 × 1981 mm) and a US one in imperial (30 × 80 in). Use the extra box for anything else that stays unpainted, such as a tiled splashback.
Coverage is the area one litre (or one US gallon) covers in one coat. It is printed on the tin and differs a lot between products, so replace the typical figure with yours. Extra adds a margin for paint left in rollers and trays and for touch-ups. The ceiling and the primer are worked out on their own lines because they are usually different products.
Tick the tin sizes your shop sells. The calculator shows the mix that leaves the least paint over and, when it uses fewer tins, the fewest-tins choice as well.
A 4 × 3.5 m room with 2.5 m walls has 2 × (4 + 3.5) × 2.5 = 37.5 m² of wall. Taking off a door (1.51 m²) and a 1.2 × 1.2 m window (1.44 m²) leaves 34.55 m². Two coats at 10 m²/L is 6.91 litres, or 7.6 litres with 10% extra: a 5 L tin and three 1 L tins, or a single 10 L tin.
Two published figures show how far apart labels can be. Sherwin-Williams puts a gallon of paint at about 350–400 ft² (8.6–9.8 m² per litre) and a gallon of primer at about 200–300 ft² (4.9–7.4 m² per litre). Dulux lists its Dulux Matt emulsion at "up to 14m2/litre" with two coats. An "up to" figure is the best case; textured, porous or patched walls take more. The defaults are 350 ft²/gal in imperial, the low end of the Sherwin-Williams figure, and 10 m²/L in metric, between that figure and the "up to" on UK emulsion tins. Primer starts at 250 ft²/gal (6 m²/L), the middle of the Sherwin-Williams primer range.
From the walls to the floor, with the same units throughout.
Strips per roll and rolls to buy, with the pattern repeat, straight or half-drop match, for Euro rolls, US double rolls or your own.
Tiles and boxes for a floor or wall, with the joint, the layout (straight, brick, diagonal, herringbone) and a waste allowance.
Kilograms or pounds of grout and the bags to buy, from the tile size, joint width and depth, by the grout makers' own formula.
Draw rooms on a grid or type their sizes, see each area and perimeter in m² and ft², and save the plan as SVG or PNG.
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Look into a shop firstWith 8 ft walls that is 384 ft² of wall. Take off a 30 × 80 in door and a 4 × 4 ft window and about 351 ft² is left. Two coats at 350 ft² per gallon need just over 2 gallons, so 2 gallons and a quart, before any extra. A metric room of 3.6 × 3.6 m with 2.4 m walls works out at about 6.3 litres for two coats at 10 m²/L.
Yes for anything large, like doors, patio doors and big windows. Small windows make little difference, and leaving them in simply gives you a little spare paint. Remember to add the door itself if you are painting it, usually with a different paint.
Follow the tin. Many wall paints ask for two coats; Dulux, for example, lists two coats for Dulux Matt. A big change of colour, a dark colour over a light one or a fresh surface can need a third coat or a primer first.
It is the best case: what one litre covers in one coat on a smooth, sound surface. Rough, porous, patched or textured walls take more paint, so real coverage is often lower. That is why the calculator starts below the labels and adds an extra allowance you can change.
The ceiling area is the room's length times its width. Tick "Paint the ceiling too" and the calculator adds a separate line for it, with its own coats and coverage, because ceiling paint is usually a different product from the walls.