Enter your room measurements, the number of doors and windows, how many coats you want and the coverage on the tin. The calculator shows how many litres you need and a sensible mix of tins.
Results are estimates for planning. Check the figures before you make a financial or health decision.
How the Paint calculator works
The calculator finds the area to paint, then divides by the coverage of your paint.
- Wall area = the perimeter of the room × ceiling height, minus openings. The perimeter is 2 × (length + width).
- Each door takes off 1.85 m² and each window 1.4 m².
- Ceiling area = length × width, added only if you choose to paint the ceiling.
- Litres = total area × number of coats ÷ coverage per litre.
The coverage box starts at 12 m² per litre, a typical figure for emulsion, but you should use the number printed on your tin. The tool then adds 10% spare, rounds up to the nearest half litre, and suggests tins from 10, 5, 2.5 and 1 litre sizes. You can enter measurements in metres or feet.
It assumes plain rectangular walls and standard-sized openings. Dark colours, rough or porous walls, new plaster and covering a strong colour can need more paint or an extra coat. Skirting boards and woodwork are not included.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Measurements in | Metres |
| Room length | 5 |
| Room width | 4 |
| Ceiling height | 2.4 |
| Doors | 1 |
| Windows | 2 |
| Paint the ceiling too | No, walls only |
| Coats | 2 |
| Coverage on the tin | 12 m² per litre |
Paint needed: 6.4 litres
| Wall area | 38.6 m² |
|---|---|
| Ceiling area | 0 m² |
| With 10% spare | 7.5 litres |
| Tins to buy | 1 × 5 L, 1 × 2.5 L |
| US gallons, with spare | 1.98 |
Tips and common mistakes
Always check the coverage on the tin, because it varies between brands and finishes. New plaster usually needs a thinned first coat, which soaks up more paint, so allow extra.
Measure the room rather than guessing, and count only the walls you will paint. If a wall is mostly glass or has a large alcove, adjust the numbers by treating it as extra doors or windows. Buying slightly too much is usually better than running out, since batches can differ in shade. For the floor or wall covering, see the Tile calculator and Wallpaper calculator calculators.
Frequently asked questions
How much coverage does paint have per litre?
It varies by paint and surface. The tool starts at 12 m² per litre, but use the figure printed on your tin.
Does it include the ceiling?
Only if you choose it. Pick yes to add the ceiling area, which is length multiplied by width.
Why does it add 10%?
A small allowance covers waste, touching up and uneven surfaces. The tool rounds the total up to the nearest half litre.