Fabric width for a gathered (dirndl) skirt.
Fuller skirts use 2\u20133\u00d7 the waist. Add length + waistband + hem separately.
A gathered skirt is made from a rectangle of fabric whose width is the waist measurement multiplied by a fullness ratio. The ratio decides how full the skirt looks, so a ratio of about 1.5 gives a light gather, 2 is a classic fullness, and 3 gives a very full, dramatic skirt. Enter your waist and the ratio to find the width of fabric needed.
Lightweight fabrics such as cotton lawn, voile, and rayon can take a higher ratio and still drape well, while thick or stiff fabrics bunch up at the waist and look best with a lower one. Divide the total width by the width of your fabric to see how many panels you will need to join.
Remember the seam allowances when you cut, and the extra length for the hem and the waistband. Sew two or three rows of long gathering stitches, pull the threads evenly, and distribute the gathers before you attach the waistband, so the fullness is spread around the waist.
Gathered skirts use a lot of fabric, so check the cost before you buy. If the pieces have a print with a direction, you will need extra to match them across the seams.