How to use it
- Choose Measure by: Room size for a room, or Wall area if you know the total area of the walls.
- Enter the size of the room, or the wall area, then the Doors and Windows with their sizes.
- Type the Number of coats and the Coverage per litre printed on your paint can.
- Tick Paint the ceiling too or Use primer first if they apply. Then read Paint to buy and the cans of each size.
How the litres are calculated
For a room, the calculator first measures the walls: the perimeter (twice the length plus the width) times the height. The area of the doors and windows is then taken off, because it is not painted.
The remaining area is multiplied by the number of coats and divided by the coverage of your paint. Ten per cent is added for waste: what stays in the tray, on the roller and in the brush, and the drips.
Litres = (wall area − doors and windows + ceiling) × coats ÷ coverage per litre × 1.10
The result is rounded up to a tenth of a litre.- Coverage is per coat. Paint that covers 10 m² a litre covers 5 m² of wall when it takes two coats.
- Primer counts as one more coat on the same surfaces.
- In imperial units the result is in gallons: 1 gallon is 3.785 litres, and the coverage is in square feet per gallon.
Can sizes and what the figure leaves out
The cans shown are the sizes of one Turkish maker's wall paint: 2.5, 7.5 and 15 litres. The DYO Dinamik Soft Mat product page lists exactly these sizes and gives 12 to 16 square metres per litre for one coat. The number of cans of each size is the amount to buy divided by the can, rounded up to whole cans.
The calculator assumes an ordinary wall that takes paint evenly. Some surfaces need more paint than the can states.
- Rough, porous or freshly plastered walls soak up more paint: allow for less coverage than the can states.
- A light colour over a dark one usually needs a primer or a third coat.
- Metallic, textured and exterior paints have their own coverage, so check that paint's data sheet.
Worked example: a 4 × 3.5 × 2.5 m room
The walls are 2 × (4 + 3.5) × 2.5 = 37.5 m². One door of 0.9 × 2.1 m (1.89 m²) and two windows of 1.2 × 1.2 m (1.44 m² each) take off 4.77 m², which leaves 32.7 m² to paint.
Two coats at 10 m² per litre need 6.546 litres. With 10 % waste that is 7.2006 litres, so the calculator shows 7.3 litres to buy. One 7.5-litre can is enough, and so are three 2.5-litre cans.
| Step | Result |
|---|---|
| Wall area, less doors and windows | 32.7 m² |
| Paint for two coats | 6.5 litres |
| With 10 % waste, rounded up | 7.3 litres |
| Cans of 2.5 litres | 3 |
| Cans of 7.5 litres | 1 |
Frequently asked questions
Where do I find the coverage of my paint?
On the label of the can and in the paint's technical data sheet, usually as square metres per litre for one coat. If you cannot find it, start with 10 m² per litre, which is a cautious figure.
Why does the calculator add 10 % waste?
Some paint stays in the tray, on the roller and in the brush, and some is lost in drips and at the edges. Ten per cent covers that. It is a rule of thumb, not a standard.
Should I count the ceiling?
Only if you paint it. Tick the box and, in Room size mode, the room's length times its width is added to the walls. In Wall area mode, type the ceiling area in its own box.
Does the calculator work in gallons?
Yes. Choose Imperial units: the sizes are then in feet, the coverage in square feet per gallon, and the cans are 1 and 5 gallons.
Is the result exact?
No. It is an estimate for planning. The surface, the roller and the colour change how much paint a wall takes, so buy a little extra or keep what is left for touch-ups.
Sources
- DYO, Dinamik Soft Mat: pack sizes 2.5, 7.5 and 15 litres; 12 to 16 m² per litre for one coat
- Benjamin Moore, Ben Interior Matte: coverage 400 to 450 sq ft per gallon, 1 or 2 coats
Figures and text last checked on Tuesday, November 10, 2026.