How many 2x4 ceiling tiles do you need in a 15x30 room?

57-60 ceiling tiles measuring 2'x4 would cover a 15'x30' ceiling.

For the least amount of trimming, place 4 tiles at 4' (trimming 1') for a total of 15'. For the 30' side, it would take 15 tiles at 2' each for a total of 30'. 4 tiles wide x 15 tiles long = a total of 60 tiles.

To use the minimum number of tiles, one could run the tiles the opposite direction, although this would involve more trimming.

In this case, place 8 tiles at 4' (trimming 2' total) for a total of 30'. For the 15' side, place 8 tiles at 2' (trimming 1' total) for a total of 15'. If the cuts were precise, the end tiles (cut in half) could each be figured as 1/2, for a total of 57 pieces with no waste/scrap.

A total of 64 tiles would be an ample amount to cover any miscuts, in most situations.