The short answer
Litres = wall area × coats ÷ coverage per litre. Dulux’s general guide is about 16 m² per litre for its wall and ceiling paints, and 2 coats. A 3 × 4 m bedroom with 2.4 m walls, one door and one window needs about 3.9 litres for the walls by our arithmetic, so a 4 litre tin.
How to work out paint for a room
- Wall area: add the length and width, double it, then multiply by the height. A 4 × 3 m room with 2.4 m walls has 2 × (4 + 3) × 2.4 = 33.6 m² of wall.
- Take off doors and windows: 1.67 m² for each standard door, and the measured size of each window.
- Multiply by the coats and divide by the coverage: 30.49 m² × 2 ÷ 16 = 3.81 litres, rounded up to 3.9.
- For the ceiling, multiply the length by the width, then by the coats, and divide by the ceiling paint’s coverage.
That’s the same method Dulux describes: surface area divided by the coverage rate per litre, multiplied by the number of coats. The calculator rounds each figure up to the next 0.1 litre so it never comes out short.
Paint coverage and tin sizes
Show the figures and sources the calculator uses
| Figure | Value used | Source |
|---|---|---|
| Wall paint coverage | About 16 m² per litre per coat | Dulux paint calculator guide |
| Ceiling paint coverage | About 16 m² per litre per coat | Dulux paint calculator guide |
| Primer coverage | About 14 m² per litre (shown with every result) | Dulux paint calculator guide |
| Coats | 2, the ideal for most Dulux paints | Dulux paint calculator guide |
| Door deduction | 1.67 m² (2040 × 820 mm) | Hume Doors standard internal size |
| Window deduction | 1.44 m² (1.2 × 1.2 m) | Our working figure; measure your windows |
| Tin sizes | 1, 2, 4, 10, 15 litres | Wash&Wear and Ceiling White sizes listed at Bunnings |
Checked 6 October 2026. Tinted colours can come in fewer tin sizes. The suggested tin mix is our own rule: it keeps leftover paint and the number of tins down. No prices are included.
When to buy a little more
Rough, porous or freshly patched walls can take more paint, and a big colour change can need an extra coat. Dulux says to check the spread rate on the back of the tin; a lower spread rate means more paint. If your tin gives a different figure, change the coverage assumption above.
Painting help in Bankstown
For scuffed walls, small patched areas and skirting, see painting touch-ups in Bankstown, or plaster wall repairs if the wall needs patching first. In NSW, painting work valued at more than $5,000 including materials and GST needs a contractor licence, as the handyman scope guide explains. The handyman cost guide has published hourly rates and task prices.
Questions about this tool
Should I deduct doors and windows?
Yes, for a closer figure. This calculator takes off 1.67 m² per door (a standard 2040 × 820 mm internal door) and 1.44 m² per window unless you change the sizes. If you’re painting the doors or frames too, that’s extra paint, usually a different product.
Do I need a licence to paint a room in NSW?
Painting work is one of NSW’s licensed trade categories. A contractor needs a licence to carry out, advertise or contract for residential painting work valued at more than $5,000 including labour, materials and GST.
Sources and date checked
- Dulux Australia — paint calculator and coverage guide
- Hume Doors — internal door standard sizes (Humecraft HMC9)
- Bunnings — Dulux Wash&Wear Low Sheen Vivid White sizes
- Bunnings — Dulux Ceiling White sizes
- NSW Government — building and trade work categories (painting work)
Information checked 6 October 2026. Guides explain the source’s published scope; a job needs its own assessment.