How the amount is worked out
Wall area is 2 × (length + width) × height. We subtract 1.9 m² for each door and 1.4 m² for each window, add the ceiling if you ticked it, multiply by the coats, then divide by the coverage per litre. Ten percent is added on top.
Painting tips
- Buy all the paint for one room at once, so the colour matches from one tin to the next.
- Fill cracks and sand glossy walls before you start. A good surface saves paint.
- Putting down new floors too? Estimate the tiles with the tile and flooring calculator, or convert areas with the unit converter.
Frequently asked questions
How do I calculate how much paint I need?
Add up the wall area, take away doors and windows, multiply by the number of coats and divide by the coverage of one litre. Add about 10% extra.
How much does a litre of paint cover?
Most emulsion paints cover 10–12 square metres per litre per coat (roughly 400 square feet per US gallon). Check the tin, because rough or dark walls use more.
How many coats do I need?
Two coats give an even finish in most cases. Painting light over dark, or over bare plaster, may need a primer and a third coat.
What sizes are doors and windows assumed to be?
A standard door is taken as 1.9 square metres and a window as 1.4 square metres. If yours are very large, add an extra window or door to the count.
Should I paint the ceiling with the same paint?
Ceilings usually get a flat white ceiling paint. Tick the ceiling box to include it in the area if you will use the same paint.