To estimate yardage (45 inch wide fabric) needed for lengthwise layout, double the length of panel and divide by 36. Example, fabric width is 45 inches and length of panel needed is 49 inches, so 49X2=98; 98/36=2.72 or roughly 2 3/4 yards of fabric is called for. Note: lots of woolens and some linens are 55 to 60 inches wide, so be sure to check to make sure you need to cut on the length. You might be able to use the crosswise layout.
If you really need to know the minimum amount of fabric you can get by with (maybe it's very narrow or it is $29.99 a yard and you don't want to buy any extra!) I suggest creating two paper (use taped together newspapers) panels. Lay them side by side, top to bottom. Now move them until they would fit on the width of your chosen fabric as shown. If you haven't yet decided on the fabric, jot down the different results for common fabric widths: 35, 45, 55 and 60 inches are standard widths.
You will also need 1 inch non roll elastic, cut to your waist measurement plus one inch or cord/ ribbon for drawstring cut to full hip plus at least 12 inches for tying.
Pre-shrink your fabric (If it's washable...some woolens are not, check the bolt end to see if it is a dry clean only fabric. Remember to make a note of any special care requirements you find on the bolt of fabric!)
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. Fold fabric lengthwise, matching selvages. Measure along fold for the length of the panel. Pin or mark. Measure across the width of the fabric from that point HALF the top width of the panel. Mark or pin. From the bottom corner of the fold measure along raw edge ONE HALF the bottom panel width. Mark or pin. Draw or pin guidelines and cut the first panel. Using this still folded panel as your pattern, cut the second panel from along the fold. Now cut the other two...they will actually be two sets of half gores. Match top edges and selvages, right sides together and sew. Press seam open. (These seams will be the side seams.) Repeat for second set of half gores. Now you have four panels, proceed as for the crosswise layout gored skirt.