Question: how to work out how many square meters of tiles i need?
Answer: Find the area of the room. Length x Width = Area. ... 
Find the area of a single tile in square feet. Add the width of the grout lines. ... 
Divide the area of the room by the area of a single tile.
Add 10% for waste. Consider adding up to 30% for intricate designs and larger tiles.
Round up.