Paint calculator
Work out how much paint you need for a room. Measure the walls, take off doors and windows, add the ceiling if you're doing it, and see how many litres that is for your number of coats, plus the mix of tins that leaves the least paint over.
Walls
Measure the floor along two walls that meet, and the height from skirting board to ceiling. The calculator adds up all four walls.
Width × height of each wall in metres. Add a row for each wall or part of a wall, like a chimney breast side.
Doors and windows
A standard UK internal door is 762 × 1981mm. Leave out small windows if you'll be cutting in around them anyway.
Filled in from the room's length and width.
Paint
Check the tin for its coverage: most emulsions say 10 to 13 m² per litre on smooth walls. Use less for new plaster, rough walls or a big colour change.
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How this calculator works
- Wall area: for a whole room, the perimeter times the height: 2 × (length + width) × height. A 4 × 3.5m room with 2.4m walls is 2 × 7.5 × 2.4 = 36m². Wall by wall, it adds up width × height for each row.
- Doors and windows are taken off: one standard door is about 1.5m² and a 1.2m square window is 1.44m², leaving 33.06m².
- Paint: area × coats ÷ coverage. Two coats at 12m² per litre is 33.06 × 2 ÷ 12 = 5.51 litres. The extra for waste (10% by default) covers what's left in the tray, on the roller and on the walls of the tin, so 6.06 litres.
- Tins: it tries every mix of the tin sizes you ticked and picks the one that wastes least, without loading you up with small tins: each extra tin counts as about half a litre of waste, because small tins cost far more per litre. For 6.06 litres that's a 5L and a 2.5L tin (7.5 litres), rather than a 2.5L and four 1L tins. Untick sizes your shop doesn't sell and it picks again.
The ceiling is worked out the same way (length × width), as separate paint, because ceilings usually get a different white. Walls and ceiling each get their own tins.
Paint coverage guide
Coverage varies by paint and surface. These are typical figures from UK paint makers' tins; your tin's own figure is the one to use.
| Paint or surface | m² per litre |
|---|---|
| Matt or silk emulsion, smooth wall | 10 to 14 |
| Trade or contract matt emulsion | 12 to 16 |
| One-coat emulsion | 8 to 10 |
| Mist coat on new plaster (watered down) | 8 to 10 |
| Textured walls or Artex | 6 to 8 |
| Satinwood or gloss on wood | 14 to 18 |
Tips
- Two coats is normal. Even "one coat" paints usually need two when you change colour, especially going from dark to light.
- New plaster drinks paint. Let it dry fully (it goes an even pale pink), then give it a mist coat of watered-down matt emulsion before the top coats. Set coverage lower for that coat.
- Buy it all at once. Tints can vary slightly between batches, so get every tin of a colour together and box them (mix them in a bucket) if you're using more than one.
- Keep a little back. A small leftover is handy for touch-ups. Write the colour and room on the lid.
- Doing woodwork too? Skirting boards, door frames and doors take far less paint: a 750ml tin of satinwood usually does a room's woodwork.
- Papering or tiling instead? Use the wallpaper calculator or the tile calculator.
- Panelling a wall? Plan the battens with the wall panelling calculator first, then paint the wall and panels together.
Frequently asked questions
How much paint do I need for a room?
For an average 4 × 3.5m bedroom with 2.4m ceilings, one door and one window, two coats on the walls take about 5.5 litres before waste. With 10% extra that's about 6 litres: a 5L and a 2.5L tin. The ceiling adds about 2.3 litres for two coats, before the extra.
How many square metres does a litre of paint cover?
Most emulsions cover 10 to 14m² per litre per coat on smooth, sealed walls. Rough, textured or new surfaces take more. The tin shows the maker's figure.
How many coats of paint do I need?
Usually two. One may do if you're repainting the same colour on a sound wall with a good-quality paint. Going from a dark colour to a light one, or painting new plaster, can need three including the mist coat.
How do I measure a wall for paint?
Measure the width along the bottom and the height from the top of the skirting board to the ceiling, in metres. Multiply them for the area. For sloping or odd-shaped walls, split them into rectangles and add a row for each in "Wall by wall".
Should I take off doors and windows?
Yes, for full doors, windows and patio doors. Leave small things like sockets and switches in, as the leftover helps with cutting in.
How much paint for a ceiling?
Multiply the room's length by its width. A 4 × 3.5m ceiling is 14m², so two coats at 12m² per litre need about 2.3 litres, so a 2.5L tin if you're careful, or 3 litres with 10% extra.
Does it save what I type?
No. Everything is worked out in your browser, and nothing is stored or sent anywhere.
Results are estimates to help you plan. Coverage depends on the paint, the surface and how you apply it, so always check the tin and follow the manufacturer's instructions.