Paint calculator
Work out how many litres of paint a room needs after doors and windows, and which 2.5, 5 or 10 litre tins to buy.
Floor to ceiling. 2400 mm is 2.4 m.
A whole number. Add one for a mist coat on new plaster.
Results
- Paint needed
- 4.7 LCoats: 2, coverage 14 m²/L
- Area to paint
- 33.1 m²
- Tins to buy
- 1 × 5 L0.3 L left over
Coverage, door and window sizes
Use the figure on your tin. Rough, porous or bare walls take more paint.
Every door and every window is counted at these sizes. Measure one of each, frame included if you will not paint it.
Tins in the mix: 2.5 L, 5 L, 10 L. The mix is the fewest tins that hold enough paint without leaving more than a 5 L tin over.
Estimate only. Check the product label and the building regulations where you live before you buy or build.
Quick answer
Multiply the room perimeter by the wall height, take off the doors and windows, multiply by the number of coats and divide by the coverage on the tin, such as up to 14 m² per litre for a matt emulsion. A 4 × 3.5 m room with 2.4 m walls, one door and one window has 33.1 m² of wall, so two coats at 14 m² per litre take 4.7 litres: one 5 litre tin.
How to use the paint calculator
- Choose Room size and type the length and width of the floor and the wall height in metres, or choose Wall area if you have already added up the walls you will paint.
- Enter the number of doors and windows. Each door counts as 762 × 1981 mm, the most popular UK standard door size according to one door maker, and each window as 1200 × 1200 mm, an example size; change both under Coverage, door and window sizes.
- Set the number of coats and choose Walls and ceiling if you are painting the ceiling too. The ceiling gets its own tins, so you can buy a different colour or product for it.
- Check the coverage against your tin. The calculator starts at 14 m² per litre, the ‘up to’ figure Dulux gives for its matt emulsion; lower it for rough or porous walls.
- If you measured the room in feet, choose Imperial. The lengths, areas and door and window sizes switch to feet, inches and square feet, while the coverage stays in m² per litre as printed on the tin, and the paint and the tins stay in litres.
How do you work out how much paint you need?
Find the wall area, take off the doors and windows, multiply by the number of coats and divide by the coverage per litre. For a rectangular room the wall area is the perimeter, 2 × (length + width), times the wall height. Door and window sizes in centimetres become square metres when you divide width × height by 10,000.
The suggested tins are the fewest that hold enough paint without leaving more than one 5 litre tin over. So 4.7 litres is one 5 litre tin, just over 5 litres is one 10 litre tin rather than a 5 and a 2.5, and 10.5 litres is a 10 and a 2.5 litre tin.
wall area = 2 × (length + width) × wall heightdoor area (m²) = width (cm) × height (cm) ÷ 10,000area to paint = wall area − doors × door area − windows × window areaceiling area = length × widthpaint (litres) = area to paint × coats ÷ coverage (m² per litre)How many tins of paint do I need for a room?
A 4 × 3.5 m room with 2.4 m walls, one door and one window needs 4.7 litres for two coats on the walls: one 5 litre tin. Every row below uses the same assumptions: 2.4 m walls, one 762 × 1981 mm door, one 1200 × 1200 mm window, two coats and 14 m² per litre.
| Room (m) | Walls (m²) | Paint (litres) | Tins to buy |
|---|---|---|---|
| 3 × 3 | 25.9 | 3.7 | 1 × 5 L |
| 3.5 × 3 | 28.3 | 4.0 | 1 × 5 L |
| 4 × 3.5 | 33.1 | 4.7 | 1 × 5 L |
| 4.5 × 3.5 | 35.5 | 5.1 | 1 × 10 L |
| 5 × 4 | 40.3 | 5.8 | 1 × 10 L |
| 6 × 4 | 45.1 | 6.4 | 1 × 10 L |
Walls only, computed with the calculator. Ceilings add 1.3, 1.5, 2.0, 2.3, 2.9 and 3.4 litres for the same rooms: one 2.5 L tin up to 4.5 × 3.5 m, one 5 L tin for the two larger rooms. From 4.5 × 3.5 m the walls need just over 5 litres, so the mix moves to one 10 L tin; a 5 L and a 2.5 L tin also hold enough and leave less over.
Worked examples
A 4 × 3.5 m bedroom, walls and ceiling
The walls are 2 × (4 + 3.5) × 2.4 = 36 m². One door (76.2 × 198.1 cm = 1.51 m²) and one window (120 × 120 cm = 1.44 m²) leave 33.1 m² to paint. Two coats at 14 m² per litre take 33.1 × 2 ÷ 14 = 4.7 litres, so buy one 5 litre tin, with 0.3 litres left over.
The ceiling is 4 × 3.5 = 14 m². Two coats take 14 × 2 ÷ 14 = 2 litres, one 2.5 litre tin. In all you paint 47.1 m² with 6.7 litres.
A newly plastered 3.5 × 3 m room with a mist coat
Bare new plaster gets a sealing coat of thinned emulsion before the two finishing coats, so set Coats to 3. The walls are 2 × (3.5 + 3) × 2.4 = 31.2 m², and one door and one window leave 28.3 m². Three coats at 14 m² per litre take 28.3 × 3 ÷ 14 = 6.1 litres.
The calculator suggests one 10 litre tin, with 3.9 litres left over. A 5 litre and a 2.5 litre tin hold 7.5 litres and leave less over, but that is two tins; compare the prices where you shop. The calculator counts the mist coat like any other coat.
How many square metres does a tin of paint cover?
Dulux rates its matt emulsion at up to 14 m² per litre. Its advice is to multiply the area by the number of coats and divide by the figure on the tin, so the calculator reads 14 m² per litre as the area one litre covers in one coat: a 2.5 litre tin covers up to 35 m² once, or 17.5 m² with two coats. ‘Up to’ is the most you can expect, so a rough or porous wall covers less. Use the figure on your own tin when you have it.
| Tin | One coat covers | Two coats cover |
|---|---|---|
| 2.5 L | up to 35 m² | up to 17.5 m² |
| 5 L | up to 70 m² | up to 35 m² |
| 10 L | up to 140 m² | up to 70 m² |
The same emulsion is also listed in 3, 6, 7 and 7.5 litre tins. The calculator leaves those out of the mix and suggests 2.5, 5 and 10 litre tins only.
Do I need a mist coat on new plaster?
Yes, if the plaster is new, bare and absorbent. Dulux’s instructions for its matt emulsion are to seal such a surface with the same emulsion thinned 10% with water, or to use a sealer for plaster if the surface is very porous. That thinned first coat is what decorators call a mist coat.
Add it to Coats in the calculator: 3 instead of 2 for a mist coat and two finishing coats. Dulux says to leave 2 to 4 hours between coats. If you use a separate plaster sealer instead, work it out on its own with Coats set to 1 and the coverage printed on that product.
Questions
How many tins of paint do I need for a bedroom?
One 5 litre tin covers the walls of a 4 × 3.5 m bedroom with 2.4 m walls. After one door and one window there are 33.1 m² to paint, and two coats at 14 m² per litre take 4.7 litres. Painting the 14 m² ceiling as well takes 2 more litres, which is one 2.5 litre tin. A 3 × 3 m box room needs 3.7 litres for the walls, still one 5 litre tin.
How much does a 2.5 litre tin of paint cover?
Up to 35 m² for one coat, or 17.5 m² for two, at the up to 14 m² per litre Dulux gives for its matt emulsion. That is enough for two coats on one wall 7 m long and 2.4 m high, which is 16.8 m² and takes 2.4 litres. Coverage differs between products and finishes, so check the figure on your own tin.
How much paint do I need for a ceiling?
About 2 litres for a 4 × 3.5 m ceiling, so one 2.5 litre tin. The ceiling is 14 m², and two coats at 14 m² per litre take 2 litres. To work out your own, multiply the room length by its width, then by the number of coats, and divide by the coverage per litre. Choose Walls and ceiling in the calculator to see the ceiling tins listed apart from the wall tins.
How many coats of emulsion do I need?
Two coats, the number Dulux gives for its matt emulsion, with 2 to 4 hours between them. Add a third coat for the mist coat when you paint new, bare plaster. If the label on your tin gives a different number, follow the label and set Coats to match; the calculator scales the litres and the tins with it.
Should I buy a 10 litre tin or two 5 litre tins?
The calculator suggests one 10 litre tin as soon as you need more than 5 litres, because it picks the fewest tins that leave no more than one 5 litre tin over. So 5.1 litres becomes one 10 litre tin, and 10.5 litres becomes a 10 and a 2.5. If you would rather have less left over, a 5 and a 2.5 litre tin hold 7.5 litres; compare prices where you shop.
Can I enter the room size in feet?
Yes. Choose Imperial and the room, door and window sizes switch to feet and inches, and the area to paint is shown in square feet. The coverage stays in m² per litre, as printed on the tin, and the paint and the tins stay in litres, so there are no gallons to convert. The same room gives the same litres in feet as in metres.
Sources
- Dulux UK, How much paint do you need (checked 19 October 2026)Measure the surface, subtract windows and doors, multiply by the number of coats, then divide by the square metres per litre on the tin or in the product information.
- Dulux UK, Dulux Matt (checked 19 October 2026)Matt emulsion for walls and ceilings: coverage up to 14 m² per litre; 2 coats, 2 to 4 hours apart; seal new, bare, absorbent surfaces with the emulsion thinned 10% with water; tins from 2.5 to 10 L.
- JB Kind, Interior Folding Doors (checked 19 October 2026)The most popular UK standard door size: 1981 mm high × 762 mm wide × 35 mm deep.
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