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Project guide

How much paint do I need for a room?

Measure the walls, take off doors and windows, multiply by the number of coats and divide by 12. Here is the rule, a worked example and a calculator that does it for you.

Updated Based on manufacturer guidance, sources below

The short answer

For a typical repaint, allow 1 litre of emulsion for every 6 m² of wall: that is 2 coats at 12 m² per litre per coat. A 4 x 3.5m room with a 2.4m ceiling needs about 5.5 litres for the walls and 2.3 litres for the ceiling, so one 10 litre tin covers both if they are the same colour.

The formula

  • Wall area (m²) = perimeter x ceiling height - 1.6 m² per door - 1.5 m² per window
  • Ceiling area (m²) = length x width
  • Litres = area x number of coats / 12

Worked example

A 4 x 3.5m bedroom, 2.4m high, with one door and one window, 2 coats:

  • Perimeter: 4 + 3.5 + 4 + 3.5 = 15m
  • Walls: 15 x 2.4 = 36 m², minus 1.6 (door) and 1.5 (window) = 32.9 m²
  • Wall paint: 32.9 x 2 / 12 = 5.5 litres
  • Ceiling: 4 x 3.5 = 14 m², so 14 x 2 / 12 = 2.3 litres
  • Total 7.8 litres: one 10L tin, or separate tins if the ceiling is white and the walls are a colour (a 5L tin for the walls and a 2.5L tin for the ceiling).

Work it out for your job

Change the measurements and the quantities update straight away.

Wall area to paint
32.9 m²
Ceiling area
14 m²
Paint needed
7.8 litres (2 coats)
Walls / ceiling
5.5 L / 2.3 L
In 10L tins
1 x 10L
Or smaller tins
2 x 5L

Your list

  • 1Matt emulsion, 10L tins
  • 1Interior filler
  • 3Decorator's caulk
  • 12 inch brush
  • 13 inch brush
  • 1Roller and tray set
  • 1Masking tape rolls
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Materials checklist

  • Matt emulsionWalls and ceiling. Buy the ceiling white separately if the walls are a colour.
  • Interior fillerFor holes and cracks. Sand it smooth before painting.
  • Decorator's caulkSeals gaps along skirting boards and around door frames.
  • 2 inch and 3 inch brushesFor cutting in at corners, edges and around sockets.
  • Roller and trayA medium-pile sleeve suits most emulsions on smooth walls.
  • Masking tapeProtects skirting, frames and switches.
  • Satinwood or gloss (optional)For skirting boards, doors and frames.

You'll also need

  • Dust sheets
  • Sandpaper or a sanding block (120 grit)
  • Sugar soap to wash the walls
  • Filling knife
  • Roller extension pole and a spare sleeve for a second colour
  • Paint kettle for cutting in

Step by step

  1. Measure the roomMeasure the length and width of the floor and the height from floor to ceiling, in metres.
  2. Work out the wall areaMultiply the perimeter by the height, then take off about 1.6 m² for each door and 1.5 m² for each window.
  3. Choose the number of coatsTwo coats for a normal repaint, three on new plaster (a thinned mist coat plus two full coats), one for a same-colour refresh.
  4. Convert to litresMultiply the area by the number of coats and divide by 12 m² per litre. Do the ceiling separately if it is a different colour.
  5. Round up to tinsRound up to the tin sizes you can buy, and keep a little back for touch-ups.

Tips from the manufacturers

  • Plan on 12 m² per litre per coat, not the figure on the tin. Manufacturers quote "up to" figures: about 13 m² per litre for retail matt emulsion and up to 17 for trade vinyl matt (Dulux). Real walls, rollers and porous patches use more.
  • New plaster needs a mist coat first: emulsion thinned with water so it soaks in and seals the surface (Dulux). Choose 3 coats in the calculator.
  • Dulux describes two full coats as the normal finish. Big colour changes, especially light over dark, can need a third.
  • If you are buying more than one tin of a colour, mix them together in a bucket (boxing) so any slight batch difference does not show.

Mistakes to avoid

  • Working from the "up to" coverage on the tin and running out halfway round the room.
  • Forgetting that the ceiling and walls are often different colours, so one big tin is not enough of either.
  • Skipping the mist coat on fresh plaster, which can make the paint peel.
  • Painting before filler and caulk are fully dry and sanded.

Frequently asked questions

How many m² does a litre of paint cover?

Matt emulsion manufacturers quote up to about 13 m² per litre per coat for retail paint and up to 17 m² for trade vinyl matt. SmartBuild plans on 12 m² per litre so there is enough for porous or uneven walls.

How much paint do I need for a 3 x 3m bedroom?

With a 2.4m ceiling, one door and one window, the walls are about 25.7 m². Two coats need about 4.3 litres for the walls and 1.5 litres for the ceiling, so about 5.8 litres in total.

Do I need two coats of paint?

Usually, yes. Two full coats is the normal finish. One coat can be enough when you are refreshing the same colour; new plaster needs a mist coat plus two coats.

Should I take doors and windows off the wall area?

Yes. A standard door with its frame is about 1.6 m² and an average window about 1.5 m². In a small room that can save a litre or more.

How much paint do I need for a ceiling?

Multiply the floor length by the width to get the ceiling area, then multiply by the number of coats and divide by 12. A 4 x 3.5m ceiling needs about 2.3 litres for two coats.

Sources

Quantities are estimates for typical jobs, using the coverage figures above. Products vary, so check the data sheet for the product you buy, and talk to a professional for structural, electrical or gas work. SmartBuild is independent and not affiliated with any of the manufacturers listed.

How much plaster do I need to skim a room?A finish skim is about 2mm thick. British Gypsum says a 25kg bag of Multi-Finish covers about 10 m² at that thickness. How much plasterboard do I need?Each standard 2400 x 1200mm sheet covers 2.88 m². Divide your area by that, add 10% for cuts, then work out the screws, tape and plaster to go with it. Stud wall materials list: what do I need?A timber stud partition is CLS studs at 400mm centres between a head and sole plate, boarded both sides. Here is everything on the list and how much of each.

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