Selecting the tile calculation method you would like to use in a room can be done from the Tile & Patterns section of the Home tab
or from within the Tile Editor.
Please note that a room with tile in it must be selected for this option to be available.
How to Change the Tile Calculation Method
1. Select a room that has tile in it
2. In the Tile & Patterns section of the Home tab click Calculation
3. From the drop down select Area or Tile Count