This depends on the area of the tile. For example, if the tiles were exactly one square foot each, then you would need about 260 of them. I say "about" 260 because - although that would give you the correct footage - it does not account for needing to cut the tiles, fit them around pillars, doorways and such.
For a decent approximation, assuming the room is rectangular:
If there are large areas of the room that won't be getting floored (eg. a pillar or stairwell), you can subtract their area (this time rounding down) from the count in order to cut back on the need for supplies purchased.
You would need 56 tiles to do the floor
123 tiles
forty
6.75 Tiles
16 square tiles
400
each tile is one square foot so you need 55 tiles
about 28
585
24 of them.
100
Assuming the tiles are 1 foot squares, you would need 10*15 = 150 tiles.