Paint Calculator - How Much Paint Do I Need for a Room
How much paint do you need
Doors are counted as 1.9 m² (20 ft²) and windows as 1.4 m² (15 ft²) each; raise the extra percentage for rough or very absorbent walls.
How to work out how much paint you need
Paint is sold by the can and used by the square metre, and the label's coverage figure assumes a smooth, primed wall and a single coat. This calculator turns room dimensions into paintable area, subtracts doors and windows, multiplies by coats and a touch-up allowance, and tells you how many cans of the size you choose to buy.
Steps
- 1 Pick metres or feet, then enter the room's width, length and wall height.
- 2 Count the doors and windows, set the number of coats and the coverage printed on the paint can; tick the ceiling if you are painting it.
- 3 Choose the can size you plan to buy. The result shows the area, the litres or gallons needed and the number of cans.
Wall area and openings
Wall area is the perimeter of the room times the wall height: 2 × (width + length) × height. Doors and windows are subtracted at typical sizes — about 1.9 m² for a door and 1.4 m² for a window — because measuring each one rarely changes the number of cans. Skirting boards, cornices and the small areas above and below windows are left in; they are what the touch-up allowance is for.
Coverage and coats
Coverage is printed on the can as square metres per litre or square feet per gallon and typically runs 10–12 m²/L (350–400 ft²/gal) for emulsion on a smooth wall. New plaster, rough textures and dark colours being covered by light ones absorb more and need lower coverage or an extra coat. Two coats is the norm for a colour change; one may do when repainting the same shade.
Choosing can sizes
Buying one large can is usually cheaper per litre than several small ones, but leftover paint only has value if you will use it for touch-ups. The calculator rounds up to whole cans of the size you select; try two sizes and compare — 9 litres might be one 10 L can or two 5 L cans with less waste.
Primer, ceilings and trim
Primer is a separate product with its own coverage; run the calculator again with one coat and the primer's figure if you need it. Ceilings use the room's floor area and are included with the checkbox. Woodwork — doors, frames, skirting — is painted with a different product and is not part of this estimate.