Buy the right amount of paint the first time.
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Measure the room's perimeter and wall height to get the wall area, then subtract about 20 sq ft (1.9 m²) per door and 15 sq ft (1.5 m²) per window.
One gallon of paint covers about 350–400 sq ft per coat, and one litre about 10–12 m². Two coats are normal; dark colours and new plaster may need three.
| Units | Feet & inches |
| Room length (ft or m) | 12 |
| Room width (ft or m) | 10 |
| Wall height (ft or m) | 8 |
| Doors | 1 |
| Windows | 2 |
| Coats | 2 |
| Paint the ceiling too? | No |
| Coverage (sq ft per gallon or m² per litre; 0 = typical) | 0 |
| Paint needed | 1.71 US gallons (6.5 L) |
| Area to paint | 299.3 sq ft · 27.8 m² |
| Buy | 1 gallon + 3 quart(s) |
| Coats | 2 |
| Coverage used | 350 sq ft per gallon |
1.71 US gallons (6.5 L).
| Units | Metres & centimetres |
| Room length (ft or m) | 4 |
| Room width (ft or m) | 3.5 |
| Wall height (ft or m) | 2.4 |
| Doors | 1 |
| Windows | 2 |
| Coats | 2 |
| Paint the ceiling too? | No |
| Coverage (sq ft per gallon or m² per litre; 0 = typical) | 0 |
| Paint needed | 6.2 litres (1.64 gal) |
| Area to paint | 334.8 sq ft · 31.1 m² |
| Buy | 2 × 5 L tins (or 3 × 2.5 L) |
| Coats | 2 |
| Coverage used | 10 m² per litre |
6.2 litres (1.64 gal).
With 8 ft walls, one door and two windows: about 1.9 gallons for two coats — buy 2 gallons.
About 350–400 sq ft per coat on smooth, primed walls.
A typical 4 × 4 m bedroom needs about 5–6 litres for two coats on the walls.
Yes on bare plaster, wood or drastic colour changes; many paints include primer.