To determine how many tiles you need to tile your ceiling, multiply the room's length by its width to arrive at the square footage and then add about 10 percent for extras. Divide the square footage by the number of square feet (square meters) of tile in each box (it varies by manufacturer) to figure out how many boxes of tile to buy..

Though the simplest method to install ceiling tiles on an existing ceiling is to glue them directly to the existing dry wall, sometimes it isn't possible. In those cases, you might staple the tiles to furring strips (narrow strips of wood) installed on the ceiling or lower the ceiling with a suspended ceiling system.

When applying adhesive to the back of a ceiling tile before attaching it to the ceiling, always use a putty knife. Place a dab of glue in each of the four corners and in the center of the tile.

To find the midpoint of a ceiling, first measure and mark the midpoint of each wall. Then stretch a chalk-box line between two opposite midpoints and mark; repeat for the other two midpoints to get the ceiling midpoint.

When installing ceiling tiles, always start in one corner of the room. Calculate the size of the corner tile and cut it to size.

Square ceiling tiles are constructed to lock together, with two grooved edges and two tongued edges, known as tongue and groove construction.

After installing a new tile ceiling, you should install cove molding along the ceiling's edges. This concave-profile molding will give your new tile ceiling a nice, finished look.

To install a tile ceiling using furring strips, nail 1 X 2 or 1 X 3 (2.5cm X 5 cm or 2.5 cm X 7.5 cm) strips at right angles across the ceiling joists and along the edges of the ceiling using 6d common nails. The tiles will then be nailed to the strips.

Using a staple gun and staples, attach the ceiling tiles to the furring strips. Be sure to staple at an angle through each tile's grooved edge, then slide in the next tile's tongued edge so the tiles will lock into place.

Always check the manufacturer's instructions before deciding which size staple to use when installing a tile ceiling.