How to Calculate a Ceiling Grid

Measure the length and width of the room using the tape measure and record the measurements on paper. Measure width parallel to the ceiling joists and measure the length perpendicular to the ceiling joists. The room we will use in our example is 15.75-feet wide and 27.25 feet long. Our tiles will be common 2-by-2 feet square tiles.

Calculate the width of the side wall tiles. Divide room width by tile width and round down. Multiply the result by tile width and subtract the result from room width. Divide the remainder by 2 to obtain the cut tile width on either side of the room .

Example: 15.5 feet / 2 feet = 7.75; round it down, and you get 7. 7 x 2 = 14 feet. 15.5 - 14 = 1.5 feet. 1.5 feet / 2 = .75 feet or 9-inch tile on the left and right sides of the room.

Calculate the length of the end wall tiles. Divide room length by tile length and round down. Multiply the result by tile length and subtract from room length. Divide the remainder by 2 to obtain the cut tile length on either end of the room. Example: 27.25 feet / 2 = 13.625; round down equals 13 feet. 13 feet x 2 = 26 feet . 27.25 feet - 26 feet = 1.25 feet. 1.25 feet / 2 = .625-feet. The tile length at the end walls is .625-feet or 7.5 inches.

Adjust the grid according to the calculated cut tile lengths. Measure a main beam from the first cross-tie slot toward the end for the room end cut tile length and mark the main beam for cutting. Mark and cut the first main beam for each run the same way.

Adjust the grid according to the calculated cut tile widths. At each end wall, measure from the left and right corners the distance of the side wall cut tile width and mark the end wall. This gives you the starting and ending points for the first main beam run. Use these marks to snap a chalk-line on the ceiling joists for placement of hangers.