When purchasing your fabric yardage, use a tape measure to wrap around the table, from the center of the underside and around the sides until you meet your initial mark. You'll want about 6 additional inches of fabric to account for edges and any user error.
Once you have your fabric, measure the width of your table and transfer your measurements to the fabric. Cut a length of fabric about two inches wider than the width of your table surface. It's important to leave the extra inch around all sides for a clean finish on the edges.
Editor's Tip: A lightweight fabric works best with this technique.