Building
Paint Calculator
Litres and cans from your wall sizes, minus doors and windows.
How this calculator works
Enter your wall length and height, or a total area if you already know it. The calculator deducts 1.8 square metres per door and 1.5 per window, multiplies by your number of coats and divides by a spread rate of 16 square metres per litre.
That spread rate is the industry standard for quality acrylic on a sealed smooth wall. Rough render, bare plaster and strong colour changes cover less area per litre.
Cans are suggested as a mix of 10 litre and 4 litre sizes to minimise leftover paint, and costs come from typical July 2026 pricing: budget $12 to $20 per litre, mid range $20 to $35, premium $35 to $55.
| Surface | Coverage per litre | Notes |
|---|---|---|
| Sealed smooth walls | 16 m² | The standard rate |
| New plasterboard | 10 to 12 m² | First coat soaks in, use sealer undercoat |
| Rough render or texture | 6 to 10 m² | Surface area is much larger than it looks |
| Ceilings | 14 to 16 m² | Flat ceiling paint |
| Tier | Per litre | What you get |
|---|---|---|
| Budget | $12 to $20 | Fine for low traffic rooms and rentals |
| Mid range | $20 to $35 | Better coverage and washability |
| Premium | $35 to $55 | One coat hiding claims, stain resistance |
Frequently asked questions
How much paint do I need per square metre?
One litre covers about 16 square metres per coat on a sealed smooth wall. At two coats, budget one litre for every 8 square metres of wall.
Do I really need two coats?
Almost always yes for a colour change or new work. One coat can be enough when repainting the same colour in good condition. Dramatic colour changes, especially over dark walls, may need three.
Do I subtract doors and windows from the area?
Yes, and this calculator does it automatically at 1.8 square metres per door and 1.5 per window. Skip the deduction for a single small window, the margin will absorb it.
Is premium paint worth it?
For high traffic areas, kitchens and bathrooms, usually yes: better washability and coverage can save a whole coat. In low traffic bedrooms a mid range paint does the job.
How much paint for a whole house interior?
A typical 3 bedroom home has 250 to 350 square metres of wall. At two coats that is roughly 30 to 45 litres of wall paint, plus ceiling paint and trim enamel.
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