How much paint do I need for a wall

1. Surface area of the surface(s) to be painted.
2. Spreading rate of the paint being used.
3. The number of coats needed.

Example:

1. To paint the living room walls - not including the ceiling. The walls are 3m high, with a total of 18m of wall length (allowing for doors and windows) the surface area is 3m x 18m = 54m².
2. The walls are currently painted and are in good condition. Resene Zylone Sheen - low sheen acrylic is selected and has a theoretical spreading rate of 11 square metres per litre.
3. Because the walls are previously painted and in good condition, only two coats of Zylone Sheen will be required.