Paint Calculator CA
Estimate how many litres of paint you need for a room from its size, the number of coats and the paint’s coverage.
How it works
Enter the room length, width and wall height, subtract the area of doors and windows, then set the number of coats and the paint’s coverage. The calculator estimates the litres of paint needed.
Frequently asked questions
How much paint do I need for a room?
Multiply the room perimeter by the wall height to get the wall area, subtract doors and windows, multiply by the number of coats, then divide by the paint’s coverage per litre. A typical 4×3 m room needs about 5 litres for two coats.
What is the coverage per litre of paint?
Most matt emulsion paints cover about 12–14 m² per litre per coat on a smooth wall. Gloss covers a little more and masonry paint a little less. Check the tin, as brands vary slightly.
Does Dulux paint cover more than other brands?
Coverage is broadly similar across major emulsion brands, including Dulux — around 12–14 m² per litre per coat. The tin states the exact figure for that specific product.
How many coats of paint do I need?
Two coats is standard. Use a third coat over bare plaster, very dark existing colours, or when painting a light colour over a dark one.
How do I calculate paint for the ceiling?
Multiply the room length by its width to get the ceiling area, then divide by coverage per litre and multiply by the number of coats, exactly as you would for walls.
How much paint for one wall?
Multiply that wall’s width by its height, subtract any door or window, multiply by coats, and divide by coverage per litre.
How many litres are in a gallon of paint?
A US gallon is about 3.79 litres and a UK gallon about 4.55 litres. If a tin is sold in gallons, multiply by the right figure before using a per-litre coverage rate.
Should I buy extra paint?
Yes — add roughly 10% for touch-ups and uneven areas, and keep tins from the same batch so the colour is consistent.
Paint Calculator
Working out how much paint to buy is simple once you know two things: the area you are painting and how far a litre of your paint goes. This calculator does the arithmetic, but the method below shows exactly how the figure is reached so you can sanity-check it before you buy.
How much paint do I need?
The core formula is: paint needed = wall area ÷ coverage per litre × number of coats. Wall area is the room perimeter multiplied by the wall height, minus the area of large doors and windows.
Paint coverage per litre
Coverage varies by paint type and surface. Most emulsion (matt) paints — including popular brands such as Dulux — cover roughly 12–14 m² per litre per coat on a smooth, previously painted wall. As a rough imperial guide, that is about 350–400 sq ft per US gallon.
| Paint type | Coverage per litre (per coat) |
|---|---|
| Matt / emulsion | ~12–14 m² |
| Silk / satin | ~13–15 m² |
| Gloss / eggshell | ~15–16 m² |
| Primer / undercoat | ~10–12 m² |
| Masonry (exterior) | ~6–10 m² |
How many coats?
Two coats is standard for a durable, even finish. Allow a third coat when going over bare plaster, a strong colour, or when a light shade is covering a dark wall.
Worked example
A 4 m × 3 m room with 2.4 m walls has a perimeter of 14 m, giving 14 × 2.4 = 33.6 m² of wall. Subtract about 3 m² for a door and window to get 30.6 m². For two coats that is 61.2 m² of coverage; at 13 m² per litre you need about 4.7 litres — so a 5 litre tin.
Buy a little extra
Add around 10% for touch-ups and uneven surfaces, and buy tins from the same batch number so the colour matches exactly.
Results are estimates for general guidance in Canada and may not reflect the latest local rates, fees or rules. Check official sources before making decisions.