Measure the length and the width of the ceiling and divide it by two. The fabric will hang from the edges to the center of the ceiling, so each panel will need to be half the total width and length of the area.
Add 15 to 20 percent to the calculation of the ceiling size. In order for the fabric to drape and create the desired whimsical effect, ensure you have more fabric than needed. These numbers will indicate the length of fabric that you need to purchase.
Measure the width of the fabric that you are using for the ceiling drapes. Determine how many widths of fabric you will require to cover the length and width of the ceiling. Multiply the numbers by two so that you purchase the proper number of panels for each side of the room.