Hi guys.. I'm planning to paint my new subsale flat with 650sqft and 3 rooms.. May I know how much litres that I need for painting ..?

Primer - For undercoat (1 coat), is it 1 big bucket (18 litres) is enough?
Color - For topcoat (2 coats), is it require 1 big bucket or need 2 big buckets?

I have asked hardware shop, but for topcoat, some said 1 big bucket is enough and another said its require 2 big buckets..

now confuse..