Depending on the look you are trying to achieve you will want to order extra width in addition to the size of your window unless you want the curtain to hang flat in which case a couple of extra inches will make sure the glass is completely covered.
For a ripple affect order a curtain approx. 1.3x the width. To achieve soft folds order 1.5x and for gathers 2x
For example, if your window measures 48 inches wide and you want to achieve soft folds then order either 1 panel 72 inches (48 + 24 = 72) or 2 panels 36 inches wide.
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