How much cans for a big wall?

[manimal]

Hi. So i have this wall, wich is about 20 square metres
How much cans i shall get to paint all over it? the pice consist of ~ 4 to 5 colors, and is more like simple comix styile, no gradients i mean.
Maybe lets put it this way, doesn anyone knows, how many square metres could one 400ml or 600ml can cover? So i could calculate the whole thing.
Any thoughts on this?

the wall itself:

[Drink86]

666 will be nice

[giantmonster]

thanks for sharing...