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Paint calculator

Work out how much paint you need for the walls and ceiling of a room, or for any area you know in m². You get the litres for your coats and the tins to buy, so you waste as little as possible.

Paint tins, roller and brush on a dust sheet in front of a pale blue wall

2.4 m is typical. Measure floor to ceiling.

doors
windows

For walls and ceiling together, this is the wall paint. The ceiling uses ceiling paint.

coats

Two coats is standard. One may do over a similar colour.

Your result

Paint needed

5.9 litres

35.7 m² painted, 2 coats

Area painted
35.7 m²
Tins to buy
1 × 5 L + 1 × 2.5 L (7.5 L)least paint left over
  • Coverage is a cautious planning figure. Rough, dark or porous surfaces use more, and a big colour change may need an extra coat.

Add this to your project shopping list, then print it or take it to the merchant.

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How to use the paint calculator

  1. Choose what you are painting: the walls of a room, the ceiling, both, or one area where you know the m².
  2. Type in the room length and width. For walls, add the wall height and the number of doors and windows.
  3. Pick the type of paint: emulsion for walls, ceiling paint, satinwood or gloss for woodwork, masonry paint, or woodstain.
  4. Set the number of coats. Two is standard.
  5. Fresh, bare plaster? Turn on New bare plaster? Add a mist coat. The mist coat is added to the total.
  6. Check the tins in the result, then tap Add to shopping list or Share link to keep it.

Why use this calculator

It takes off doors and windows for you. Each door is 1.5 m² and each window 1.2 m². You only need to count them, not measure them.

It copes with new plaster. Bare plaster soaks up paint, so the first coat is a thinned-down mist coat. We work out how much paint and how much water that takes, and add the paint to your total.

It rounds to real tin sizes. Wall and ceiling paint is worked out in 2.5 litre and 5 litre tins, and woodwork paint in 750 ml and 2.5 litre tins. We pick the mix with the least paint left over. The working shows every step, so you can check it.

How we worked it out

Your numbers, step by step. This updates as you change the calculator.

  1. Walls: distance round the room = 2 × (4 m + 4 m) = 16 m; × 2.4 m high = 38.4 m²
  2. Take off 1 door (1.5 m² each) and 1 window (1.2 m² each) = 2.7 m², leaving 35.7 m² of wall
  3. Walls (emulsion): 35.7 m² × 2 coats ÷ 12 m² per litre = 5.95 litres
  4. Walls tins: 5.95 litres needs 1 × 5 L + 1 × 2.5 L = 7.5 L
  5. Total paint = 5.95 litres over 35.7 m²

The formula

  • Walls: the distance round the room, 2 × (length + width), × the wall height, minus the doors and windows.
  • Ceiling: length × width.
  • Litres: area × number of coats ÷ coverage in m² per litre.
  • Mist coat (new plaster): area ÷ 12 gives the litres of mix. 70% of that is paint and 30% is water. The paint is added to your total.
  • Tins: we choose the mix of tin sizes that covers the litres with the least paint left over, then the fewest tins.

For a 4 m by 4 m room, 2.4 m high, with one door and one window, the walls are 16 m round. 16 × 2.4 = 38.4 m², minus 1.5 m² for the door and 1.2 m² for the window leaves 35.7 m². Two coats at 12 m² per litre is 35.7 × 2 ÷ 12 = 5.95 litres. Two 2.5 litre tins is only 5 litres, so the best buy is one 5 litre and one 2.5 litre tin, 7.5 litres in total.

What we assume

  • Coverage per coat: 12 m² per litre for emulsion, ceiling paint, satinwood and gloss. Manufacturers quote up to 13 to 17 m² per litre on smooth, sealed surfaces, so 12 is a cautious planning figure.
  • Masonry paint: 12 m² per litre on smooth render and 5 m² per litre on textured render or pebbledash. Textured surfaces vary a lot, so treat it as a minimum.
  • Woodstain: 6.4 m² per litre. This comes from decking stain only. Rough or sawn timber can take far more.
  • Doors and windows: a door is 1.5 m² (a standard 1981 × 762 mm door). A window is 1.2 m², a typical double casement. There is no standard window size, so this is a guess.
  • Mist coat: 12 m² per litre of mixed paint, one mist coat and then your normal coats. No UK manufacturer publishes a mist coat figure, so this is a rule of thumb.
  • Tin sizes: 2.5 and 5 litres for wall, ceiling and masonry paint. 750 ml and 2.5 litres for satinwood, gloss and woodstain. Other sizes exist, such as 1 litre and 10 litres, but we leave them out. Check what your shop sells.
  • Ceiling height: 2.4 m unless you change it.

Tips

  • Mix all the tins for one wall in a bigger container before you start. Colour can vary a little between tins, and mixing them evens it out.
  • Keep what is left over for touch-ups. Write the colour name and the date on the lid.
  • For skirting boards and doors, choose One wall or area and Satinwood or Gloss, then type in the area. Woodwork paint is bought in smaller tins.
  • Coverage drops on rough, dark or porous surfaces, and a big colour change may need a third coat. If you are changing a dark wall to white, check what the tin says.
  • Doing the whole room? Use the square metre calculator to measure odd shapes, and the wallpaper calculator if one wall will be papered instead.

FAQs

How much paint do I need for a 4 m by 4 m room?
For the walls, about 6 litres for two coats, with a 2.4 m ceiling height, one door and one window. That is 35.7 m² of wall at 12 m² per litre. The best mix is a 5 litre and a 2.5 litre tin. Add the ceiling and the total is about 8.6 litres.
How many m² does 1 litre of paint cover?
We use 12 m² per litre per coat for emulsion on a smooth, painted wall. Tins often say up to 13 or 14, and some trade paints up to 17, but that is the best case. Masonry paint on smooth render is also 12, and on textured render or pebbledash it is only 5.
How many coats of paint do I need?
Two coats is standard for walls and ceilings. New plaster needs a thinned mist coat first, then two full coats. One coat may do over a very similar colour, but check the result.
How much paint do I need for a 12 m² wall?
For two coats of emulsion, 2 litres, so one 2.5 litre tin. That is 12 m² × 2 coats ÷ 12 m² per litre. If the plaster is new and bare, a mist coat adds 0.7 litres of paint, so the total is 2.7 litres and you need a 5 litre tin.
What is a mist coat, and how much water do I add?
It is a thinned-down first coat for new, bare plaster. We use 70% paint and 30% water, so 12 m² takes 1 litre of mix, which is 0.7 litres of paint and 0.3 litres of water. Dilutions vary by paint, so follow the tin if it says something different.
Do I take off doors and windows when I work out paint?
Yes. The calculator takes off 1.5 m² for each door and 1.2 m² for each window. Large windows or patio doors will be bigger, so for those use the single-area option and type in your own m².

Last reviewed: 6 November 2026 · How we calculate · Report an error