A room with a 16 m wall perimeter, 2.5 m walls and 5 m² of doors and windows needs 6.4 litres for two coats at 11 m² per litre. Add 10% and buy about 7.0 litres, or 1.8 US gallons.
The method
Paintable area = perimeter × height − openings. Here 16 × 2.5 − 5 = 35 m². Divide by the coverage per litre and multiply by the number of coats.
Coverage varies by product and surface; the label gives m² per litre. We use 11 m² per litre as an example.
Add a margin
Walls are uneven and rollers hold paint, so buy about 10% more than the calculation. A second coat on a similar colour can use less; a dark-to-light change needs more, so one coat is 3.2 litres, but plan for primer too.
Other rooms
The table gives the volume for other perimeters, in litres and US gallons. Use the paint coverage calculator to enter your own room and coverage.
| Perimeter (m) | Litres | US gallons with 10% margin |
|---|---|---|
| 12 | 4.5 | 1.3 |
| 16 | 6.4 | 1.8 |
| 20 | 8.2 | 2.4 |
| 24 | 10.0 | 2.9 |
FAQ
Should I paint the ceiling too?+
The calculation covers walls. For the ceiling, use the paint coverage surface calculator with its area.
How many coats do I need?+
Usually two. One coat can be enough when repainting in a similar colour with a quality paint.