How to calculate how much paint you need
Add up the area of your walls, subtract doors and windows, multiply by the number of coats, then divide by the paint's coverage rate: Paint = (Wall area − openings) × coats ÷ coverage per litre. Wall area for a rectangular room is 2 × (length + width) × height.
How much paint for a room? By room size
Paint for the four walls of a typical room with one door and one window, two coats, at standard coverage (11 m² per litre / 350 ft² per US gallon). Ceilings are not included. Rooms with more openings need slightly less; textured or bare walls need more.
| Room (2.4 m high) | Wall area | Paint |
|---|---|---|
| 3 × 3 m | 25.6 m² | 4.7 L |
| 3 × 4 m | 30.4 m² | 5.5 L |
| 4 × 4 m | 35.2 m² | 6.4 L |
| 4 × 5 m | 40 m² | 7.3 L |
| 5 × 5 m | 44.8 m² | 8.1 L |
| 5 × 6 m | 49.6 m² | 9 L |
| 6 × 6 m | 54.4 m² | 9.9 L |
| Room (8 ft ceiling) | Wall area | Paint |
|---|---|---|
| 10 × 10 ft | 285 ft² | 1.6 gal |
| 10 × 12 ft | 317 ft² | 1.8 gal |
| 12 × 12 ft | 349 ft² | 2 gal |
| 12 × 14 ft | 381 ft² | 2.2 gal |
| 14 × 16 ft | 445 ft² | 2.5 gal |
| 16 × 20 ft | 541 ft² | 3.1 gal |
How much does a tin of paint cover?
At a typical 11 m² per litre (350 ft² per gallon). The two-coat column is the area you can actually finish, since most walls need two coats.
| Tin | 1 coat | 2 coats |
|---|---|---|
| 1 L | 11 m² | 5.5 m² |
| 2.5 L | 27.5 m² | 13.8 m² |
| 5 L | 55 m² | 27.5 m² |
| 10 L | 110 m² | 55 m² |
| Can | 1 coat | 2 coats |
|---|---|---|
| 1 gal | 350 ft² | 175 ft² |
| 2 gal | 700 ft² | 350 ft² |
| 5 gal | 1750 ft² | 875 ft² |
How many coats?
Most jobs need two coats for an even finish. Go to three when painting a light colour over a dark one, or onto fresh plaster. A primer/undercoat may be needed on bare or patchy surfaces — count it as an extra coat.
Tips to buy the right amount
- Buy a little extra (round up) so you have enough for touch-ups and don't run out mid-wall.
- Coverage drops on rough, porous or textured surfaces — reduce the coverage number for those.
- Painting the ceiling too? Add its area (length × width) to the wall area.
How many litres of paint do I need for a 4 × 4 m room?
About 6.4 litres for two coats on the walls, assuming a 2.4 m ceiling, one door, one window and 11 m² per litre coverage. Buy a 5 L tin plus a 2.5 L, or two 5 L tins if you want spare for touch-ups.
How much paint do I need for a 12 × 12 room?
About 2 gallons for two coats on the walls of a 12 × 12 ft room with 8 ft ceilings, one door and one window. Two gallons covers it.
How much does 5 litres of paint cover?
About 55 m² for one coat, or 27.5 m² for two coats, at a typical 11 m² per litre. Check the tin — coverage varies from roughly 10 to 14 m² per litre by brand and finish.
How much primer do I need?
Treat primer as one extra coat, but use the primer's own coverage figure — it's often lower, around 8–10 m² per litre, because bare surfaces absorb more. Enter it as a separate one-coat calculation above.
Does this include the ceiling?
No — it covers the four walls. Add the ceiling area (length × width) manually if you're painting it.
What coverage should I use?
Check the tin. Typical emulsion is 10–12 m² per litre (about 350 ft² per US gallon) per coat; primers and textured paints cover less.
Metric or US gallons?
Switch units to feet and the coverage/price flip to US gallons (1 gal ≈ 3.785 litres).