About this calculator
Buy too little paint and you risk a mismatched second batch; buy too much and you waste money. Enter the room's length, width and height in metres, the number of doors and windows and how many coats you plan, and get the litres and the number of tins.
The coverage figure is on the tin: typically 10 to 14 square metres per litre. The calculator assumes 12 if you leave it blank, and a standard door and window size.
Worked examples
Real numbers, worked out by the same calculator. Press “Use these numbers” to try one above.
4 m × 3 m room, 2 coats, walls only
- Paint needed
- 5.1 litres
- 5 litre tins to buy
- 2
- Left over
- 4.9 litres
- Wall area to paint
- 30.6 m²
A 4 m × 3 m room with 2.4 m walls needs about 5.1 litres for 2 coats: buy 2 × 5 litre tins.
Show the working
- Wall area = 2 × (length + width) × height = 2 × (4 + 3) × 2.4 = 33.6 m².
- Take off doors (1 × 1.6 m²) and windows (1 × 1.4 m²): 33.6 − 3 = 30.6 m².
- Ceiling not included.
- Paint = area × coats ÷ coverage = 30.6 × 2 ÷ 12 = 5.1 litres.
- Door and window sizes are typical averages. Rough or dark walls may need more.
Same room including the ceiling
- Paint needed
- 7.1 litres
- 2.5 litre tins to buy
- 3
- Left over
- 0.4 litres
- Wall area to paint
- 30.6 m²
- Ceiling area
- 12 m²
A 4 m × 3 m room with 2.4 m walls needs about 7.1 litres for 2 coats: buy 3 × 2.5 litre tins.
Show the working
- Wall area = 2 × (length + width) × height = 2 × (4 + 3) × 2.4 = 33.6 m².
- Take off doors (1 × 1.6 m²) and windows (1 × 1.4 m²): 33.6 − 3 = 30.6 m².
- Add the ceiling, 4 × 3 = 12 m².
- Paint = area × coats ÷ coverage = 42.6 × 2 ÷ 12 = 7.1 litres.
- Door and window sizes are typical averages. Rough or dark walls may need more.
Large living room, 3 coats
- Paint needed
- 12.3 litres
- 5 litre tins to buy
- 3
- Left over
- 2.7 litres
- Wall area to paint
- 45.1 m²
A 6 m × 4.5 m room with 2.5 m walls needs about 12.3 litres for 3 coats: buy 3 × 5 litre tins.
Show the working
- Wall area = 2 × (length + width) × height = 2 × (6 + 4.5) × 2.5 = 52.5 m².
- Take off doors (2 × 1.6 m²) and windows (3 × 1.4 m²): 52.5 − 7.4 = 45.1 m².
- Ceiling not included.
- Paint = area × coats ÷ coverage = 45.1 × 3 ÷ 11 = 12.3 litres.
- Door and window sizes are typical averages. Rough or dark walls may need more.
How the amount is worked out
Wall area = 2 × (length + width) × height. A typical door (1.6 m²) and window (1.4 m²) are taken off. Paint needed = area × coats ÷ coverage. With the ceiling included, its area (length × width) is added before multiplying by the coats.
Allow a margin
- New plaster or bare wood soaks up a first mist coat (thin the first coat)
- Dark colours over light, or the reverse, can need three coats
- Rough, textured or very porous walls use more paint
- Keep a little over for touch-ups: left-over paint is useful
Ceilings and woodwork
Ceiling paint is usually a different product from wall paint. Run the calculator with the ceiling option and use the ceiling area line, or run it twice. Skirting boards, doors and window frames use gloss or satin paint, which you buy in small tins.
Frequently asked questions
How much paint do I need for a room?
Wall area × coats ÷ coverage. A 4 m × 3 m room with 2.4 m walls and two coats needs about 5 litres.
How much does one litre cover?
Most emulsion covers 10 to 14 m² a litre per coat. Check the tin.
How many coats do I need?
Two for most jobs. One if you repaint the same colour in good condition, three for big colour changes.
Do I paint behind furniture?
Include all the walls you will paint. The calculator treats the walls as continuous.
Are the door and window sizes exact?
No, they are typical averages (1.6 and 1.4 m²). Measure your own if they are unusually large.
Formulas tested against hand-worked answers. Last reviewed 29 September 2026. These calculators do arithmetic only; they are not financial, tax or legal advice.