Paint Calculator (Litres Needed)

🎨 Paint Calculator

Litres of paint for a room or wall, allowing for coats, coverage and openings.

Surface area (m²)

Number of coats

Coverage (m²/L)

Openings to deduct (m²)

Paint Needed

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Net Area

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Total Painted Area

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Tins (5 L)

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⚠️ litres = (area × coats) ÷ coverage. Coverage 10–12 m²/L for emulsion; less for textured or porous surfaces and for the first coat on bare plaster. Use a primer/mist coat on new surfaces. Verify before professional use.

Standards & method

✓ Independently verified 12 July 2026

Basis

First principles

Method

Coverage-rate take-off. Spreading rate (m²/L) is a manufacturer figure and varies hugely with substrate porosity.

Core formula

litres = (area × number of coats) / spreading rate

Why this matters

Spreading rate on a porous or previously unpainted surface can be half the tin’s stated figure. Deduct openings, and remember that a colour change usually needs two coats regardless of the arithmetic.

Independently verified

12 July 2026 — Formula re-derived from first principles and verified numerically against hand-computed reference cases, including edge cases and unit handling.

Results are for guidance. Verify against the current edition of the governing standard and have a qualified professional review before use in practice.

Paint Quantity — Method

Paint quantity is an area calculation adjusted for coats and the products spreading rate. Litres = (net surface area x number of coats) / coverage, where coverage (m2 per litre) comes from the tin - typically 10 to 12 m2/L for matt emulsion, less for textured surfaces. Subtract large openings such as doors and windows. New or porous surfaces absorb more on the first coat, so add a primer or mist coat, or simply allow extra paint for that coat.

Frequently Asked Questions

How much paint do I need for a room?⌄

Litres = (wall area x coats) / coverage. For 40 m2 of wall, 2 coats, at 11 m2 per litre that is about 7.3 litres. Deduct doors and windows from the area first.

What is paint coverage or spreading rate?⌄

The area one litre covers in a single coat, printed on the tin - typically 10-12 m2/L for matt emulsion, lower for textured, deep-colour or exterior paints.

How do I measure the wall area?⌄

Multiply each wall length by its height and add them up, then subtract the area of doors and windows. For a whole room, add the four walls (and ceiling if painting it).

How many coats do I need?⌄

Usually two top coats for an even finish, plus a primer/undercoat on bare or patchy surfaces or when changing colour drastically. Count the primer as an extra coat in the calculation.

Why does bare plaster use more paint?⌄

New plaster and porous surfaces absorb the first coat, lowering the effective coverage. Use a diluted mist coat or a primer, or add roughly 10-20% extra paint for that first coat.

Estimating Paint Quantities

Working out paint is a matter of area, coats and the products spreading rate. Get those three right and you avoid both running short mid-wall and over-buying tins you will not use.

The method

Net area (walls minus openings) x number of coats / coverage in m2 per litre. Round up to whole tins for ordering.

Surfaces and coats

Most jobs need two top coats; bare or strongly coloured surfaces need a primer or extra first coat because they absorb more. Always check the coverage figure on the specific product, as it varies a lot between matt, silk, exterior and textured paints. For wall quantities of other materials see the brick and concrete calculators.

Related: Brick, Concrete Mix.

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Paint quantity — Quick answer