If you are tall or your fabric is narrow, you will need to figure out the yardage required to achieve the fullness you prefer. After you have determined the length you need (Waist to hem, plus 3 1/2 inches), measure the width of the fabric. If it's about 45" wide and you're of average build, double your length measurement (triple it if you are a more voluptuous lady or just want extra fullness) and divide by 36 to determine the yardage to buy.
For example: Your length measurement is 49 inches and you are of average build, so 49X2=98. To figure yardage, 98/36=2.72 or roughly 2 3/4 yards of fabric per skirt. (This will make a skirt approximately 82 inches or roughly 2 1/4 yards around the hemline.) This is about the minimum size for an adult much less and you will find it hampers your stride and doesn't look right.
If you want or need a fuller skirt, it would be 49X3=147; 147/36=4.08 or roughly four yards of fabric per skirt. This makes a skirt about 132" around or 3 2/3 yards.
If your fabric is significantly narrower, say 30" wide, you should triple the length measure for average build (skirt about 85" around) and quadruple for a fuller skirt (about 115" or roughly three yards around). Figuring out the yardage to buy is the hardest part of making the alternate skirt, so don't be discouraged.
Okay, now you've got the fabric and pre shrunk it. Make sure both ends are straight (on the grain)...either snip the selvage and tear straight across, or pull a thread and cut along it. Press entire length of fabric. Measure along selvage to the length required. Snip and rip or pull thread and cut. Repeat. Now, depending on how full the skirt/narrow the fabric, you have two to four panels.
Matching selvage edges, right sides together, sew the panels together until you have a tube of material. Press seams open. Finish one raw edge and continue as for easy gathered skirt, using the finished edge to turn down for the casing.