Paint Calculator
Last updated: 12 August 2026
Work out how much paint you need for a room. Enter the room dimensions, choose your paint type and number of coats, and get the litres required for walls and ceiling.
How the calculation works
Wall area = perimeter × height, minus doors and windows. Ceiling area = length × width. We multiply the total area by the number of coats and divide by the paint coverage rate to get litres.
Coverage varies by product and surface: bare plaster and textured walls soak up noticeably more than previously painted surfaces, and a mist coat on new plaster is thinned so it goes further. Always check the tin — manufacturer figures are the authority.
Paint coverage by type
| Paint | Coverage per litre | Coats needed |
|---|---|---|
| Matt emulsion | ~12 m² | 2 |
| Silk / soft sheen | ~11 m² | 2 |
| Kitchen & bathroom | ~10 m² | 2 |
| Primer / undercoat | ~8 m² | 1 |
| Gloss / satinwood | ~14 m² | 2 over undercoat |
| Masonry paint | ~6–8 m² | 2 |
Painting new plaster
New plaster needs a mist coat first: matt emulsion thinned with about 20–30% water, which seals the surface so topcoats do not flake. The mist coat covers further than normal, then apply two full coats on top. Never use vinyl silk as a mist coat — it does not soak in.
Frequently asked questions
How much paint do I need for a room?
For a typical 4m x 3m room with 2.4m ceilings, the walls are about 34 square metres. At 12 square metres per litre with two coats, that is roughly 5.6 litres — a 5 litre tin plus a small top-up, or one 5 litre tin if you deduct doors and windows.
How many square metres does 1 litre of paint cover?
Most matt emulsion covers around 12 square metres per litre per coat. Silk is nearer 11, durable kitchen and bathroom paints about 10, and masonry paint only 6 to 8 because exterior surfaces are more porous.
How much paint is in a 5 litre tin?
A 5 litre tin of emulsion covers roughly 60 square metres in one coat, or 30 square metres in two coats — enough for the walls of an average bedroom.
How many coats of paint do I need?
Two coats is standard for emulsion over an existing painted surface. Bare plaster needs a thinned mist coat first, then two full coats. Strong colour changes, especially dark to light, can need three.
Do I need to deduct windows and doors?
For a small room with one door and one window, deducting is optional and gives you a useful safety margin. For larger rooms or lots of glazing, deduct the openings — a standard door is about 1.8 square metres and a typical window 1.5.
Related calculators
Wallpaper Calculator
Rolls needed for a room, with pattern repeat handled properly.
Plaster Calculator
Bags of multi-finish, bonding or hardwall plaster.
Plasterboard Calculator
Sheets, screws, scrim tape and jointing compound for walls and ceilings.
Estimates are for guidance only. Material dimensions, densities and coverage vary by supplier — always confirm quantities before ordering, and consult a qualified professional for structural work.