Paint Calculator (Metric)
Enter your room dimensions in metres, number of coats, and price per litre to find how much paint you need and what it will cost.
What your result means
Paint needed is the litres to buy, after figuring your wall area, knocking off about 10% for doors and windows, and applying your coats at roughly 8.6 m² of coverage per litre per coat. Paintable wall area is the surface you're actually covering. The cost is litres times your price. This is walls only — ceiling and trim are separate.
How to use this calculator
- Measure the room length and width in metres.
- Measure the ceiling height (2.4 to 3 m for most homes).
- Pick your coats: two is standard, one can work over a similar colour.
- Enter a price per litre from your paint store.
- Read the litres to buy and the estimated cost, and round up for touch-ups.
The formula
Perimeter times height gives the gross wall area. We trim about 10% for typical doors and windows, multiply by coats, and divide by 8.6 m² per litre. Litres round up to whole tins where needed.
Worked example
A 4 by 4 m room with 2.5 m ceilings has about 36 m² of paintable wall after deducting 10% for openings. Two coats needs 9 litres. At $10 a litre that's about $90 in paint.
Paint coverage and what affects it
| Factor | Rule of thumb |
|---|---|
| Coverage per litre | ~8.6 m² per coat on smooth, primed wall |
| Textured or porous walls | Drops to 6–7 m² per litre |
| Dark over light (or reverse) | Plan on 2–3 coats |
| Doors & windows | Deduct ~10% of wall area |
| Trim & ceiling | Estimate separately — different coverage |
Tips & gotchas
- Buy all your paint in one batch and box (mix) it so the colour is uniform across tins.
- Primer first on bare plaster, patches, or big colour changes — it stretches your topcoat.
- Textured walls drink more paint; drop coverage to about 7 m² per litre.
- A 4x4 m room takes roughly 9 litres for two coats.
- This covers walls only. Ceilings and trim use different products and coverage.
Frequently asked questions
How much paint do I need for a 4x4 m room?
About 9 litres for two coats on the walls, assuming 2.5 m ceilings — roughly 36 m² of wall after deducting for a door and windows.
How many square metres does a litre of paint cover?
Around 8.6 m² per coat on a smooth, primed surface. Textured or unprimed walls drop that to 6–7 m².
Do I need one coat or two?
Two is standard for an even finish and true colour. One coat can work when repainting a similar shade over a sound surface.
Does this include the ceiling and trim?
No. This calculator covers wall paint only. Ceilings and trim use different paints and coverage rates, so estimate them separately.
Should I buy extra paint?
Yes, a little. Round up to the next tin and keep some for touch-ups — matching a colour later is hard.
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Estimates only — see our full disclaimer.