Paint needed = wall area × coats ÷ coverage. A room of 4 × 3.5 m with walls 2.5 m high, one door and one window has 34.1 m² of wall; two coats at 10 m² per liter take 6.8 liters (1.8 US gallons). Enter the room in meters or feet; the calculator works in liters or gallons and shows how many cans or tins to buy.
Paint for common rooms
Walls only, one door and one window, two coats at 10 m²/L (about 400 ft²/gal):
| Room | Wall area | Paint | US gallons |
|---|---|---|---|
| 3 × 3 m, 2.4 m high | 25.4 m² | 5.1 L | 1.34 |
| 3.5 × 4 m, 2.5 m high | 34.1 m² | 6.8 L | 1.80 |
| 4 × 5 m, 2.5 m high | 41.6 m² | 8.3 L | 2.20 |
| 5 × 6 m, 2.7 m high | 56.0 m² | 11.2 L | 2.96 |
Adding the ceiling of a 4 × 5 m room adds 20 m² to paint – about 4 liters more for two coats.
How the area is worked out
- Walls: 2 × (length + width) × height.
- Doors and windows: a standard interior door is counted as 1.9 m² (about 20 ft²) and a window as 1.5 m² (about 16 ft²). For a wall of windows or a wide patio door, add more windows to the count.
- Ceiling: length × width, if you choose to paint it.
Coverage: read the can
| Unit on the can | Typical figure | Same thing in the other unit |
|---|---|---|
| m² per liter | 10–12 | 407–489 ft² per US gallon |
| ft² per US gallon | 350–400 | 8.6–9.8 m² per liter |
Coverage drops on rough, porous or textured surfaces, on fresh plaster and when the paint goes on thickly. If the walls are in poor shape, use the lower figure.
Cans and tins
US paint comes in quarts (0.95 L), gallons (3.79 L) and 5-gallon buckets (18.9 L). Elsewhere, 1 L, 2.5 L, 5 L and 10 L containers are common. A slightly larger container is often cheaper per liter, and a little extra is useful for touch-ups later – store it airtight and label it with the room and the color.
Before you start
Fill holes and cracks, sand glossy surfaces, and wash greasy areas such as kitchens. Use a primer on new or patched plaster, bare drywall and stains. Work wet edge to wet edge to avoid lap marks, and let the first coat dry fully before the second.
In the paint aisle with no signal? Once zet4u is saved on your phone, the calculator works offline.
Frequently asked questions
How do I calculate how much paint I need?
Work out the wall area: perimeter × height, minus doors and windows. Multiply by the number of coats and divide by the coverage on the can. 34 m² × 2 coats ÷ 10 m² per liter = 6.8 liters.
How much does a gallon of paint cover?
Most interior paints in the US list 350–400 square feet per gallon for one coat on a smooth wall. In metric, 10–12 square meters per liter is typical.
Do I need two coats?
Usually yes. One coat is enough only when you repaint the same color over a clean, sound surface. Changing color, especially to a darker one, often needs two or three.
Do I need primer?
On new plaster, bare drywall, stains or a big color change, yes: one coat of primer seals the surface so the paint covers evenly.
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