Paint Calculator
Calculate the amount of paint needed for your room. Enter the room dimensions and number of coats to get an accurate estimate in liters. This calculator accounts for walls only (excluding ceiling and floor).
Paint Calculation Results
How the Paint Calculator Works
The calculator starts with your wall area: it adds up all four walls by taking the room's perimeter and multiplying it by the ceiling height. It then subtracts a standard allowance for openings — about 1.5 m² per window and 2 m² per door — because you obviously don't paint glass or door leaves.
Paint (liters) = [2 × (length + width) × height − openings] ÷ 11 m² per liter × coats
The 11 m² per liter figure is the industry average for quality emulsion on a smooth, previously painted wall. One coat almost never gives full, even color, so the calculator defaults to two coats — the result is multiplied accordingly and rounded up to the nearest 0.1 liter so you never come up short mid-wall. If your walls are freshly plastered, heavily textured, or you're covering a dark color with a light one, buy 10–20% extra on top of the result, or plan for a coat of primer first.
How to Measure a Room for Painting
Measure the length and width of the room at floor level with a metal tape measure — skirting boards line up with the walls, so the floor is the most accurate place to measure. For height, measure from the top of the skirting to the ceiling line in a couple of spots; older houses often vary by a few centimeters, so use the larger figure.
Count your windows and doors rather than measuring each one — the standard allowances the calculator uses are accurate enough for ordinary rooms. Only measure openings individually if you have something unusual, like a floor-to-ceiling glass wall.
Two coats is the honest default: the first coat seals and evens the surface, the second delivers the true color and sheen. The only time one coat works is repainting a wall in the same or very similar color. Textured or porous surfaces (woodchip, bare plaster, masonry) drink noticeably more paint — expect coverage to drop from 11 m² per liter to as little as 6–8 m². If you're planning a feature wall in wallpaper instead, or tiling a splashback, subtract that wall from your total — our tile calculator covers the tiled part.
Paint Coverage by Surface Type
| Surface | Coverage per liter | Advice |
|---|---|---|
| Smooth, previously painted plaster | 11–12 m² | The calculator's default |
| Primed new drywall | 10–11 m² | Prime first or add a coat |
| Lightly textured wall | 9–10 m² | Add ~10% to the result |
| Bare plaster (mist coat) | 8–10 m² | Dilute first coat 10–20% |
| Rough masonry or brick | 6–8 m² | Add ~30% to the result |
Common Mistakes to Avoid
- Buying for one coat — nearly every color change needs two full coats for even coverage.
- Measuring a single wall and multiplying by four; rooms are rarely square, so measure length and width separately.
- Ignoring surface texture — rough or porous walls can use a third more paint than smooth ones.
- Buying the exact amount with no reserve; keep at least half a liter for touch-ups, from the same batch number.
Frequently Asked Questions
How much paint do I need for a 12x12 room?
A 12×12 ft room (about 3.7×3.7 m) with a standard 8 ft ceiling has roughly 32 m² of paintable wall after subtracting a door and a window. At 11 m² per liter and two coats, that's about 5.8 liters — a 5 liter can plus a 1 liter top-up, or about 1.5 US gallons.
How many square meters does 1 liter of paint cover?
Quality emulsion covers 10–12 m² per liter per coat on a smooth, sealed wall. On textured, porous, or bare surfaces coverage drops sharply — rough masonry can absorb enough paint to halve the figure. Always check the manufacturer's stated spreading rate; premium paints usually sit at the top of the range.
Do I really need two coats of paint?
Almost always, yes. The first coat rarely hides the old color evenly and can look patchy as it dries. The second coat delivers uniform color and full washability. The exception is repainting in the same color for freshening up — one careful coat can be enough there.
Should I subtract windows and doors from my paint calculation?
Yes — and this calculator does it automatically, using standard allowances of about 1.5 m² per window and 2 m² per door. Don't over-subtract, though: trims, reveals, and edges around openings still need paint, which is why standardized allowances beat measuring every opening precisely.