Consider Fullness to Determine Width. To avoid draperies looking like a stretched sheet, you need to consider adding fullness for additional width to cover. Curtains and draperies should be 1.5x-2x times the final measured width. More fullness will create a richer, more opulent appearance.
For example, your rod length is 100 inches, for 4-in-1 header style, total width you need order is 100 x 200% = 200 inches, then you need order 2 panels, each 100 inches width.
Visit page Measurement Finder to ensure exact size.