Paint Coverage Calculator (UK)
Work out how much paint to buy before you get to the counter. This UK paint coverage calculator takes your room size, doors and windows, number of coats and paint type, and returns the litres you need for the walls and ceiling — plus the tins to buy so you are not left with three-quarters of a 5 litre tub going off in the shed. It uses conservative real-world coverage rates rather than the best-case figure printed on the tin, works on your phone at the merchant, and there is a full worked example below.
Adds length × width
Set by paint type above; edit to use your tin's figure (3–20).
Range 0–25%. Default 10% covers cutting-in and roller loss.
Enter your room size to work out how much paint you need.
| Paint type | Working coverage (m²/L) |
|---|---|
| Standard matt emulsion (walls) | 12 |
| Silk / soft-sheen emulsion | 13 |
| Kitchen & bathroom / durable matt | 12 |
| Ceiling paint | 12 |
| Primer / undercoat | 11 |
| Eggshell (water-based) | 13 |
| Gloss / satinwood (trim) | 14 |
| Masonry paint — smooth (exterior) | 8 |
| Masonry paint — textured/rough (exterior) | 5 |
| Mist coat (thinned contract matt, new plaster) | 10 |
These are conservative on-site rates, not best-case lab figures. Coverage is classified under BS EN 13300 for interior water-borne coatings.
How to use this paint calculator
- Pick your mode — a whole room, a single feature wall, or a total area you have already measured.
- Enter the room length, width and wall height in metres, then the number of doors and windows so the tool can subtract them.
- Choose your paint type and number of coats. Two coats is standard for walls and ceilings.
- If you are painting fresh plaster, set the surface to New plaster so the tool adds a mist coat.
- Read off the litres needed and the suggested tin combination before you buy.
Measure in metres, count your openings, and let the tool convert area into litres and tins.
Coverage rates — why this tool uses conservative numbers
A tin of emulsion often quotes a spreading rate of 16 to 17 m² per litre. That is a laboratory figure on a smooth, sealed, roller-friendly surface. On a real wall, cutting-in by brush, roller loss, texture and absorption all pull the working rate down to around 10 to 12 m² per litre for standard matt emulsion. This calculator uses those working rates so you buy enough. Coverage is classified under BS EN 13300, the standard for interior water-borne coatings, but the honest number for estimating is the one you get on site, not the one on the tin.
Use 10–12 m²/L for walls, not the tin's headline figure, or you will under-buy.
Worked example — a Nottingham bedroom
Say you are repainting a bedroom in a Nottingham semi: 4.0 m long, 3.5 m wide, 2.4 m walls, one door and one window, two coats of standard matt emulsion, walls only.
- Perimeter: 2 × (4.0 + 3.5) = 15.0 m
- Gross wall area: 15.0 × 2.4 = 36.0 m²
- Openings: (1 × 1.8) + (1 × 1.4) = 3.2 m²
- Net paintable wall: 36.0 − 3.2 = 32.8 m²
- Two coats: 32.8 × 2 = 65.6 m² to cover
- At 12 m²/L: 65.6 ÷ 12 = 5.47 litres
- Plus 10% wastage: 5.47 × 1.10 = ~6 litres
You need about 6 litres. Buy a 5 litre tin plus a 2.5 litre tin (7.5 litres) so you have enough for cutting-in and a touch-up later, rather than opening a second 5 litre tin for half a wall. If you were also painting the 14 m² ceiling in two coats, that adds about 2.6 litres — a single 2.5 litre tin is just short once wastage is in, so pair it with a 1 litre tin.
For this room, roughly 6 litres of wall paint; buy slightly over so you are not caught short mid-wall.
A point most paint calculators skip
Most online paint tools take the number off the tin and give you a tidy answer that quietly under-buys, because they ignore two things: the substrate and the mist coat. Fresh plaster is porous and drinks the first coat, so it needs a mist coat first — contract matt thinned with around 10 to 20% water — before the two full coats. Skip it and the first proper coat flashes and peels. This is set out in BS 6150, the code of practice for painting buildings. Equally, a strong colour change (dark to light, or covering a feature wall) can need three coats, not two. Set the coats and surface honestly and the litres will be right.
On new plaster, add a mist coat; for a big colour change, add a coat — both change how much you buy.
How much paint per square metre?
As a rule of thumb, one litre of standard emulsion covers about 10 to 12 m² per coat on a sound wall, so you need roughly 0.08 to 0.10 litres per m² per coat. A typical 12 m² feature wall in two coats is therefore about 2 litres with wastage — one 2.5 litre tin. Rougher or more porous surfaces sit at the higher end of that range.
Budget about 0.1 litre per m² per coat and round up to the next tin size.
Frequently Asked Questions
Related tools
- Wallpaper Calculator (UK) — rolls of wallpaper by drop and pattern repeat
- Tile Calculator — number of wall and floor tiles with wastage
- Plasterboard / Drywall Calculator — boards, screws and adhesive for walls and ceilings
- All UK construction calculators
Guides worth reading
- How Much Paint Do I Need? UK Guide — coverage rates, mist coats and a room-by-room worked example
Disclaimer: This calculator gives a paint estimate for planning. Actual coverage varies with surface texture, porosity, colour change, application method and the specific product. Always check the coverage figure on your tin and buy a little over. For new plaster, use a mist coat first.