Multiply the length of the wall by the height of the ceiling.
Subtract for any doors or windows
Example: A wall that’s 4 metres long with a 3-metre-high ceiling has a wall surface area of 12 sqm
Divide the overall surface area of the wall to be painted by 6. A 12 sqm surface area, e.g. needs 2 litres of paint.
Sweet! The figures you come up with show how many litres of wall paint you need
1L of paint is enough for painting 2 layers over 4-6 sqm. The actual usage can vary based on your surface.