Checked 15 October 2026. What was checked. How these pages are maintained.
Paint quantity
Wall area = 2 × (length + width) × height, minus doors and windows. Multiply by coats. Litres = area ÷ coverage. Buy a little extra for touch-ups. Ceilings are not included unless you add them as extra area in the doors box as a negative number (or raise length/width).
Worked example
A 4 m × 3 m room, 2.4 m ceiling, four walls, no subtraction for windows: about 33.6 m². At 10 m²/L and two coats you need about 6.7 L, so two 3.7 L cans with a little waste, or a 3.7 L plus a 1 L depending on the brand.
Textured walls, dark colours, and new drywall (primer) use more. Ceilings and trim are extra. Buy the same batch if the colour is mixed in-store.
Four walls, minus the openings, times the coats
Wall area for one coat is 2 × (length + width) × height, minus the doors and windows you subtract. A room 14 ft by 10 ft with 8 ft walls has a perimeter contribution of 2 × (14 + 10) × 8 = 384 sq ft. Subtract 30 sq ft of door and window and one coat is 354 sq ft. Two coats are 708 sq ft. At the default coverage of 107 sq ft per litre, that is 708 ÷ 107 = 6.6 litres, about 1.75 US gallons. The 107 figure is roughly 400 sq ft per gallon. The number on your can wins if it disagrees. Coverage is in square feet per litre because the room boxes are in feet.
The ceiling is not in that 384. A ceiling on this room is 14 × 10 = 140 sq ft per coat. Add it by running a second calculation or by reducing the “subtract” box by 140, which is an awkward negative opening. A second run is clearer. Trim is extra again.
Colour, texture, and the same mixed can
New drywall drinks the first coat. A deep colour often needs a primer and a third coat. Textured walls cover fewer square feet per litre than the can’s smooth-wall number. If you change coats from 2 to 3, the litres scale in a straight line. Buy the custom colour from one batch. A second can mixed later can be a slightly different colour even with the same code. The floor area of the same room is the square footage calculator, and it will not tell you about paint.
Common questions
Should I paint the ceiling too?
Add length × width to the job. Put 0 in “subtract” extra, or add that area into coats on a second run.
Dark colours?
They often need a primer plus extra coats. Bump coats to 3.