Paint Quantity Calculator
Estimate the litres a room’s walls need from its size, the number of coats, and the paint’s coverage — with doors and windows taken out of the wall area.
Paint needed
Doors are treated as 1.8 m² and windows as 1.5 m². Check the tin for the spread rate — matte emulsion is often 11–13 m² per litre, but porous or freshly plastered walls drink more, especially on a first coat. This covers walls only, not the ceiling or woodwork.
Buy the right amount of paint
Guess the paint and you either run out mid-wall — risking a visible join and a batch mismatch on the top-up tin — or you finish with half-used cans you'll never quite match again. Working from the wall area, minus the openings, times the coats, gets you close on the first trip.
Coverage is the figure people most often get wrong. Fresh plaster and porous or textured walls soak up far more than a smooth, previously painted surface, especially on the first coat, so read the tin and lean toward its lower coverage number when you're unsure.
Frequently Asked Questions
How do I work out how much paint a room needs?
Measure the paintable wall area — the perimeter of the room multiplied by the ceiling height — then subtract the doors and windows you won't paint. Multiply by the number of coats and divide by the paint's coverage (the square metres one litre covers). This calculator runs that whole chain from your room dimensions.
What coverage should I enter?
Check the tin: matte wall emulsion is often quoted at 11–13 square metres per litre per coat, but it varies by brand and finish. The tool defaults to 11. If the label gives a range, use the lower number to avoid coming up short.
Why subtract doors and windows?
You don't paint the glass or the door leaf, so leaving them in would overestimate the paint. The tool treats a door as about 1.8 square metres and a window as about 1.5, and lets you set how many of each. For large picture windows or double doors, count them as two or adjust the numbers.
How many coats should I plan for?
Two coats is standard for an even, durable finish, and this is the default. Plan for a third when going light over a dark colour, painting patchy new plaster, or using a thin or strongly pigmented shade. A mist coat on fresh plaster counts as an extra coat too.
Does this include the ceiling and woodwork?
No — this estimates the walls only. Ceilings, skirting, architraves, and doors use different paints and coverage, so estimate them separately. Buy walls, ceiling, and trim paint to their own quantities rather than assuming one total covers everything.
A general estimate for wall paint from the figures you enter, using typical door and window sizes. Coverage varies with surface and technique — check the tin and buy a little spare.