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Paint Coverage Calculator — How Much Paint Do I Need?
Calculate how many litres and tins of paint you need for any room, using conservative real-world coverage rates for matt, silk, eggshell and gloss.
Measure longest wall
Measure wall adjacent to length
Standard UK ceiling height is 2.4m
Each door subtracts 1.8 m²
Each window subtracts 1.2 m²
Default: 1.8 m² for a standard UK door
Default: 1.2 m² for a standard UK window
Default: 12 m²/L for Matt Emulsion
Adds 10% extra for roller loading, cutting in and spillage
10% is standard for most painting jobs
Enter your supplier price for a cost estimate
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How We Calculate This
Our paint coverage calculator works by first calculating the total wall area of your room from its dimensions, then subtracting openings (doors and windows) to get the net paintable area. This is then multiplied by the number of coats and divided by the coverage rate for your chosen paint type.
The formula
Litres needed = (Net wall area × Number of coats) ÷ Coverage rate per litre × Wastage factor
Net wall area = (2 × (Length + Width) × Height) − (Doors × 1.8 m²) − (Windows × 1.2 m²)
For example, a room 4m × 3.5m with 2.4m ceilings, one door and two windows: Wall area = 2 × (4 + 3.5) × 2.4 = 36 m². Minus 1 door (1.8 m²) and 2 windows (2.4 m²) = 31.8 m². For 2 coats of matt emulsion at 12 m²/L: 31.8 × 2 ÷ 12 = 5.3 litres, plus 10% wastage = 5.8 litres.
Coverage rates we use
- Matt Emulsion: 12 m²/L — the most popular finish for walls and ceilings
- Silk Emulsion: 14 m²/L — wipeable finish, popular for kitchens and hallways
- Eggshell (water-based): 14 m²/L — modern acrylic eggshell for woodwork and walls
- Eggshell (solvent/oil): 10 m²/L — traditional oil eggshell, which covers noticeably less
- Gloss: 14 m²/L — high-sheen finish typically used on wood and metalwork
These are conservative real-world working rates, derated from manufacturers' published “up to” maxima (for example Dulux Trade Vinyl Matt up to 17 m²/L, Dulux Diamond Eggshell up to 16, and Dulux Quick Dry Gloss up to 16) so you don't under-order. Traditional solvent-based eggshell is the exception — its manufacturer figure is only 8-10 m²/L, so pick the right eggshell type. Actual coverage varies with surface porosity, texture and application method (brush, roller or spray); we recommend adding 10% for wastage to account for loading rollers, cutting in and general spillage.
Frequently Asked Questions
A typical UK room (3.5m × 4m with 2.4m ceilings) has around 36 m² of wall area. After subtracting a door and two windows, you're left with roughly 32 m². For two coats of matt emulsion, you'd need about 5.3 litres — so a 5L tin plus a 1L tin, or three 2.5L tins. Always round up as you can't buy part-tins.
Manufacturers quote up to 17 m²/L for trade matt emulsion (Dulux Trade Vinyl Matt and Crown Trade Vinyl Matt both state 'up to 17 m²/L'), and around 14 m²/L for retail matt. Those are best-case figures on smooth, sealed surfaces — porous, textured or freshly-skimmed plaster reduces coverage by 20-30%. Our calculator uses 12 m²/L as a conservative working figure so you don't under-order.
For most rooms, 5L tins offer better value per litre. However, if you only need slightly more than 5L, buying a 5L and a 1L tin avoids waste. For large projects, 10L tins are the most economical. Dulux, Crown and Farrow & Ball all offer various tin sizes — check your local B&Q or decorator's merchant for availability.
Yes — two coats is the industry standard for a professional finish. The first coat seals the surface and provides a base, while the second coat gives even colour and full coverage. You may need three coats when covering dark colours with light ones, or when using certain reds and yellows that have lower opacity. If your walls are new plaster, use our Primer Calculator to work out a mist coat first. For ceilings, try our Ceiling Paint Calculator.
Our calculator subtracts 1.2 m² for each standard window and 1.8 m² for each door. These are based on typical UK window and door sizes. If you have unusually large windows or patio doors, you may want to adjust by reducing the number of windows/doors and manually accounting for the difference.
Yes, exactly. Enter the room's overall length and overall width as if it were a full rectangle. Cutting a notch out of a corner does not change the perimeter: the two walls of the notch simply take the place of the wall sections they replace, so an L-shaped room has exactly the same perimeter, and therefore the same wall area, as its bounding rectangle. This is not an approximation. The thing to watch is a feature that steps in and out part-way along a wall, such as a chimney breast: that adds wall rather than removing it, two short return sides per feature. Allow for one by adding the depth of the breast to your room length measurement; the calculator doubles the length, which covers both returns.
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Last updated: July 2026
Verified against UK standards · estimates only, confirm with your supplier.