Paintable wall area: subtract openings once

A paint estimate needs the surface area being coated. For four rectangular walls, add each wall area, or multiply room perimeter by wall height when heights are equal. Add a ceiling only if you plan to paint it with the same product.

A worked example

Item	Example or check
Room	4 m × 3 m
Wall height	2.5 m
Gross walls	2 × (4 + 3) × 2.5 = 35 m²
Measured openings	3 m²
Net walls	32 m²

Check the assumptions

Do not subtract doors and windows a second time after entering a net area in the calculator. The tool cannot know whether your area is gross or net unless you keep that distinction in your own measurement notes.

With two coats and a stated 10 m²/L per-coat spreading rate, 32 m² needs 6.4 L before extra allowance. A 10% allowance makes 7.04 L. The number of tins depends on the tin volume you enter; buying two 5 L tins supplies more than that calculated target.

Before using the estimate

Texture, porosity and application affect coverage. The product label and preparation instructions take priority over a generic starting value.

Open the Paint Calculator and compare your measurements with the example.

Further reference: Publisher or manufacturer guidance. Product specifications can change; use the current label.