Paint requirements depend on net wall area, number of coats, product coverage and an allowance for waste.
1. Measure the wall area
For a rectangular 4 × 3 m room with walls 2.60 m high, the perimeter is (4 + 3) × 2 = 14 m. Gross wall area is 14 × 2.60 = 36.4 m². Do not confuse the floor area with the area you will paint.
2. Account for doors and windows
A door measuring 0.80 × 2.10 m occupies 1.68 m² and a window measuring 1.20 × 1.20 m occupies 1.44 m². Subtracting both gives 33.28 m². In practice, small openings and edges may need extra material, so use the deduction thoughtfully.
3. Add the coats
For two coats, the coverage area is 33.28 × 2 = 66.56 m². At an *illustrative* coverage rate of 10 m² per litre per coat, this requires 66.56 ÷ 10 = 6.656 litres, before allowance.
4. Allow for waste and packaging
Adding 10% gives about 7.32 litres. Actual purchases depend on available tin sizes. Check the manufacturer's stated coverage, surface porosity, existing colour, primer requirements and application method.
Common mistakes
- Using floor area instead of wall area.
- Forgetting a second or third coat.
- Confusing litres per m² with m² per litre.
- Assuming every window saves exactly its full area in paint.
Open ParedExacta to enter your own wall dimensions and openings and adjust coats, coverage and allowance.
Try it in ParedExacta
Enter your own measurements and compare the result. Actual quantities depend on your materials.