Estimate the wall and ceiling area of a rectangular room and the litres of paint needed using your product's coverage.
The calculator works out the wall and ceiling area of a rectangular room and shows the number of litres that follows from your product's stated coverage. It is a first estimate for planning an order, not a quote — it takes no account of the surface condition or the preparation the wall will need.
How to calculate the area correctly
Wall area is 2 × (length + width) × height, less the openings. In a 4 × 3 m room with a height of 2.8 m, the walls come to 39.2 m²; if doors and windows account for 3 m², the paintable area is 36.2 m². A flat ceiling adds a further 12 m².
What has to be measured separately
The calculator assumes a straight, rectangular shape. These need measuring on their own:
Recesses, beams and sloping planes.
Multi-level or dormer ceilings.
Stairwells and double-height spaces.
Openings that are excluded from the work.
Decorative or accent walls taking a different material.
Facades, where access matters more than area.
Why the real quantity differs
Manufacturers usually state 10-12 m² of coverage per litre per coat, and 8-10 m² for primer. A porous wall, a freshly repaired one, or a dark colour going light all absorb more. Two coats are standard, so the litres double.
A 4 × 3 m room, 2.8 m high, with 3 m² of openings has 36.2 m² of walls. For illustration only, 2 coats at 10 m²/L with a 10% allowance require 7.964 litres, rounded up to 8.0 L. This is not a coverage promise for a particular paint.
What to allow for
This tool estimates a rectangular room. Measure recesses, beams and complex surfaces separately. Primer, filler and labour prices are excluded. Actual use depends on the surface, application method and product.