To calculate the number of suspended ceiling tiles you need, first measure the length and width of the room in metres. Multiply these figures to find the total square metreage of the ceiling area. Next, consider the size of the ceiling tiles you plan to use — commonly, tiles are 600mm x 600mm or 1200mm x 600mm. Divide the total ceiling area by the area of one tile to determine how many tiles you’ll need. Remember to factor in a small percentage (usually around 10%) for cuts and waste.