How much paint do I need for a room?
Most people buy too much paint, or run out halfway through the second coat. Both problems come from guessing. Here is the 3-minute method that avoids both.
Step 1 — Measure the walls
Measure length, width and wall height in metres. Wall area is:
Wall area = 2 × (length + width) × height
For a 4 m × 3 m room with 2.7 m walls, that is 2 × 7 × 2.7 = 37.8 m².
Step 2 — Subtract doors and windows
You do not paint a door or a window. As a simple rule, allow 2.0 m² per door and 1.5 m² per window.
37.8 − 2.0 − 1.5 = 34.3 m² to paint.
Step 3 — Allow for coats and coverage
Most rooms need 2 coats. Most paints cover about 10 m² per litre — check your tin, it varies.
Paint needed = 34.3 × 2 ÷ 10 = 6.9 litres. Round up and buy 7 litres.
3 mistakes people make
1. Forgetting the second coat. One coat looks patchy on most walls. Always calculate for 2 unless you know one will do.
2. Painting the ceiling in the same number. Ceilings need length × width added on top — do them separately.
3. Buying the exact amount. Buy the rounded-up amount. The leftover is for touch-ups, and it is cheaper than a second trip to the shop.
Quick table — common room sizes, 2 coats, 10 m²/litre
| Room | Wall area* | Buy |
|---|---|---|
| 3 m × 3 m, 2.7 m high | 28.9 m² | 6 litres |
| 4 m × 3 m, 2.7 m high | 34.3 m² | 7 litres |
| 5 m × 4 m, 2.7 m high | 45.1 m² | 10 litres |
*After 1 door and 1 window, as above.
Common questions
How much paint for one wall?
Wall area = length × height, minus any door or window on that wall, then × coats ÷ coverage.
Does primer count?
Primer is separate. On new plaster, allow one primer coat at the same coverage, then 2 topcoats on top of that.