Let’s use an example. If the floor area is 2130 W and is 2800 L, multiply these two amounts to get your floor area in square meters.
2.130 x 2.800 = 5.964 (let’s round it up to 6 square meters to simplify)
6 meters divided by the coverage area of 1 box of tiles. One carton of 600 x 600 tiles will cover 1.08 square meters
6 / 1.08 = 5.55 ( to round up you will need 6 boxes to cover the area and you have extra should errors occur ) - redracer01
You can measure the overall size of the room and then subtract the doorways and windows to get close to the mark. You can always return unused cartons of tiles after you finish the project. - MitchellMc