Measure the whole length and width of the room (e.g. 2.5m x 3m = 7.5 sq.m.)
Measure units, baths etc. where you do not require flooring by the same method (e.g. 0.6Ocm x 2.4m = l.44sq.m.)
Deduct the units from the whole floor area
(e.g. 7.5sq.m. - 1.44 sq.m. = 6.06sq.m.)
To this total add 10-15% wastage (depending on whether you are laying tiles diagonally or straight), which gives you a total requirement of 7 sq.m.