Paint Calculator: How Much Paint Do I Need?
Work out how many litres of paint a room or the outside of a house needs, which tins to buy and roughly what it costs: walls, ceilings, woodwork and masonry, with mist coats for new plaster and extra coats for a big colour change.
No sign-up required. Free to use, with every formula shown on this page. Last reviewed October 2026.
Work out your paint
Paint Calculator
Work out how much paint a room or the outside of a house needs, which tins to buy and roughly what it costs.
1 What you're painting
Length
Width
Wall height
Woodwork = skirting boards and both sides of the doors. Window frames vary too much to include.
Measure round the house. For a gable end, add the triangle: width × height ÷ 2.
Wall surfaceHow many
Width
Height
How many
Width
Height
2 The job
Each adds one coat to the walls (new plaster adds one to the ceiling too).
Per coat. Tins quote an "up to" figure on smooth, sealed walls; this cautious default suits most walls. Use the figure on your tin if you know it.
3 Tins and prices
Untick sizes your shop doesn't sell. Prices are optional: add them to see the cost and the cheapest mix of tins.
Paint you need
0 L
Area to paint
0 m²
Coats on the walls
2
Cost
–
What you'll need
Breakdown
| Surface | Area | Coats | Litres |
|---|
Litres include 10% for rollers, trays and touch-ups.
How it's worked out: paint = area × coats ÷ coverage, plus 10% for waste, for each surface. Walls = room perimeter × height (or wall length × height outside) minus doors and windows; ceiling = length × width; skirting = (perimeter − door widths) × skirting height; doors are painted on both sides. Coverage defaults: wall and ceiling emulsion 11 m² per litre (AkzoNobel's practical spreading rate is 8,3–11), woodwork 14, masonry paint from Dulux Trade's figures for each surface. Tins: a mix with little paint left over and not too many tins, or the cheapest mix if you've entered prices for every size.
Estimates only. Coverage varies with the paint, the colour and how porous the surface is. Check the tin, and buy all your paint from the same batch.
How it works
Area, coats and coverage
How much paint you need comes down to three numbers: the area you’re painting, how many coats it needs, and how far a litre of your paint goes. The sources and assumptions behind it are on our How we calculate page.
Measure the area
Walls are the distance round the room times the height, less the doors and windows. Ceilings are length × width. For woodwork, the calculator adds the skirting boards and both sides of each door. Outside, measure round the house and add the triangles of any gable ends.
Count the coats
Most walls need two coats. New plaster needs a mist coat first, because it soaks up paint, and a big colour change often needs an extra coat. The calculator adds 10% for rollers, trays and touch-ups.
Use realistic coverage
Tins quote an “up to” figure on smooth, sealed walls. Real walls are rougher and more absorbent, so the calculator uses a cautious 11 m² per litre for emulsion and the makers’ own figures for each kind of masonry. Change it to match your tin.
Examples
How much paint for a room or a house?
The same calculator, a few common jobs. Rough surfaces like pebbledash take far more paint than smooth walls.
Illustrative only, from the calculator above with 2.4 m walls, one door (0.8 × 2 m) and one 1.2 × 1.2 m window per room unless stated. Inside: wall and ceiling emulsion at 11 m² per litre. Outside: 22 m of wall, 5.5 m high, two doors and eight windows, smooth masonry paint (14 m² per litre on render, 4 on pebbledash). All include 10% for waste. Check the coverage on your own tin.
Tips
Before you buy and paint
A little planning saves a second trip to the shop and a patchy finish.
Measure twice
Measure each wall at floor level and the height in a corner. Note the size of every door and window. Alcoves and chimney breasts add wall area, so measure round them rather than straight across.
Prepare the surface
Fill cracks, sand glossy areas and wash off dust and grease. On new plaster, let it dry fully, then use a mist coat of emulsion thinned with water as the tin says. Dark colours under light ones usually need an extra coat.
Buy and store it well
Buy all the paint at once and check the batch numbers match, as colours can vary slightly between batches. Keep the leftover for touch-ups: seal the lid firmly and store it somewhere it won’t freeze.
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Common questions
Frequently asked questions about how much paint you need
Common questions about litres, coats, coverage and tins.
How much paint do I need for a room?
For a 4 × 4 m room with 2.4 m walls, one door and one window, two coats on the walls and ceiling take about 10 litres of emulsion at a realistic 11 m² per litre, including 10% for waste: a 5 litre tin twice plus a 1 litre tin. Use the calculator for your own room.
How many coats of paint do I need?
Usually two. New plaster needs a mist coat first, and changing from a dark colour to a light one (or the other way round) often needs a third coat. One-coat paints can cover in one coat over a similar colour on a sound surface, but two coats are the safe estimate.
How much does a litre of paint cover?
Tins quote an “up to” figure: up to about 16–17 m² per litre for trade emulsions on smooth, sealed surfaces. In practice it’s lower: AkzoNobel’s own datasheet gives 8.3–11 m² per litre. Masonry paint covers about 14–16 m² per litre on smooth render but only 4–6 on pebbledash.
Do I need a mist coat on new plaster?
Yes. New plaster is very absorbent and soaks up the first coat, which can stop the paint sticking properly. A mist coat is emulsion thinned with water: check your tin for how much water to add. Let the plaster dry fully first.
How much masonry paint do I need for a house?
For the outside of a typical semi-detached house (about 106 m² of wall after the doors and windows), two coats of smooth masonry paint take about 17 litres on smooth render, but about 58 litres on pebbledash, because rough surfaces have so much more area to cover.
Is it better to buy one 5 litre tin or two 2.5 litre tins?
Larger tins are often cheaper per litre, but not always, and smaller tins avoid waste on small jobs. Enter the prices from your shop in the calculator and it works out the cheapest mix of tins for the paint you need.
Are the results exact?
No. They are estimates: coverage varies with the paint, the colour, the roller and how absorbent the surface is. The calculator is deliberately cautious and adds 10% for waste, but always check the coverage on your tin.