Enter your window size and panel width to find out how many curtain panels you need — and how much fabric to buy.
The key to great-looking curtains is fullness — the ratio of total fabric width to window width. Flat panels at 1:1 look skimpy; 2× fullness creates a classic gathered look; 2.5–3× is used for formal or luxurious drapes.
Add 6–8 inches for a standard double-fold bottom hem and 2 inches for a top header. For floor-length drapes that puddle, add an extra 6–12 inches to your drop.