On the paint can the manufacture will indicate what the sq. meters is what the can of paint will cover. Depending on the brand and type of paint you can get anywhere from 12 to 16 square meters of coverage per litre. The actual coverage will depend on the texture of the wall and the colour you are using to paint. A smooth wall will take less paint than a rough textured wall. Covering a lighter colour wall with darker colour paint will take less paint than painting a lighter colour over a dark colour wall. In addition to all that, the way you apply the paint, equipment you use to paint with and how much paint ends up on you or the floor versus the wall, will have an impact on how much paint you need.