Strip length to gather into a ruffle.
Fuller ruffles use 2.5\u20133\u00d7; soft gathers around 1.5\u20132\u00d7.
The strip for a ruffle must be longer than the edge it is sewn to, since it is gathered to fit. The length of the strip equals the length of the edge multiplied by the fullness ratio. To attach a ruffle to a 40 inch edge at a ratio of 2, cut a strip 80 inches long, which you can make by joining shorter strips.
A ratio of 1.5 gives a light ruffle, 2 is a classic ruffle, and 3 gives a very full, dramatic one. Lightweight fabrics look best with more fullness, and heavy fabrics with less. Remember to add seam allowances to the length and to each joined strip.
For the width of the strip, add the finished ruffle width and the seam allowances, and for a double layer ruffle, double the finished width. A double ruffle is folded so both sides show a finished edge and needs no hem, while a single ruffle needs the bottom edge hemmed first.
Gather by sewing two long stitches along the top edge and pulling the threads, or use a ruffler foot on your machine. Divide the strip and the edge into quarters and match the marks so the fullness is even.