What next?
Paint quantity comes from wall area. These handle the rest of the room.
What your result means
The litres figure covers every coat across the whole surface. Coverage is the number that varies most: matt emulsion on a smooth wall might reach 14 m² per litre, while the same paint over bare plaster or a dark colour can drop below 8. The figure on the tin assumes ideal conditions.
Why this one is different
Coats are multiplied into the area before the tin count, so the total is the area your brush covers rather than the size of the wall. The result is given in litres and as a count of 2.5 litre tins, with a warning line when the coverage figure you entered is outside what paint normally achieves.
The first coat on new plaster drinks far more than the tin claims
Fresh plaster is porous and absorbs paint rather than sitting on it. That is what a mist coat is for — heavily thinned emulsion that seals the surface so later coats spread properly. Skip it and you will use more paint and still get a patchy finish.
Dark-to-light changes are the other coverage killer. Going from a deep colour to white reliably needs three coats, or a tinted undercoat, no matter what the tin says about opacity.
How it works
Wall area is the room perimeter multiplied by the height. Standard allowances are deducted for openings — about 1.9 m² per door and 1.4 m² per window. That area is multiplied by the number of coats and divided by the paint’s stated coverage per litre.
How to use this calculator
- Enter the room length, width and wall height.
- Enter how many doors and windows to deduct.
- Set the number of coats — two is standard, three for a big colour change.
- Enter the coverage printed on the tin.
- Choose whether to include the ceiling.
Formula
Perimeter = 2 × (length + width). Standard deductions: 1.9 m² per door, 1.4 m² per window. Coverage is taken from the tin.
Example calculation
A 4.5 × 3.5 m room, 2.4 m high, one door, two windows, two coats at 12 m²/L:
Less openings (4.7 m²) = 33.7 m²
Two coats = 67.4 m² ÷ 12
≈ 5.6 litres — 2 × 5 L tins, or 3 × 2.5 L
Frequently asked questions
How many coats do I actually need?＋
Two over an existing similar colour. Three when going lighter, covering a strong colour, or painting bare plaster after a mist coat. One coat is only realistic when refreshing the same shade.
Should I deduct skirting and coving?＋
Only if they are being painted in a different product, which they usually are. Woodwork and trim are typically gloss or satinwood and should be calculated separately by length.
Why does my paint go further than estimated?＋
Smooth, previously painted surfaces absorb very little, and roller technique matters. Estimates deliberately run slightly conservative — running out halfway across a wall leaves a visible join.
How much does a litre of paint cover?＋
Typically 12 to 14 square metres per litre for emulsion on a prepared surface, less on bare plaster or textured walls. The tin's own figure is the one to use, since it varies by product.
Do I need a primer or undercoat?＋
On new plaster, bare wood, metal, or over a strong colour change, yes. A mist coat of thinned emulsion is standard on fresh plaster, and it counts as an extra coat when you buy.
How do I estimate paint for ceilings and woodwork?＋
Ceilings use the floor area. Woodwork is easier to estimate by running metre: skirting, architrave and doors are usually a litre or two of trim paint for an average room, bought separately from the wall colour.
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Assumptions & limitations
Every figure here comes from a simplified model. Keep these limits in mind when reading your result:
- Uses standard allowances of 1.9 m² per door and 1.4 m² per window; measure unusually large openings yourself.
- Assumes uniform wall height and rectangular rooms.
- Coverage varies with surface porosity, colour change and application method.
- Excludes primer, mist coats, woodwork and trim.