Work out how many floor tiles you need for a room, with a wastage margin for cuts and breakage.
10% wastage covers standard cuts around edges and doorways. Rooms with lots of corners, alcoves or a diagonal layout need a higher margin.
A simple rectangular room can often get by with 5–7%. An irregular room, a diagonal tile layout, or a design with borders and insets can push actual usage well past 10% — round up rather than order twice.
Tiles are sold by the box, not individually. Once you have a target count, round up to the nearest full box for your chosen tile — your vendor can tell you tiles-per-box for the exact product.