Pull the futon cushion off of the frame and place it on a flat surface, such as the floor, and measure the length, width and thickness of the cushion.
Divide the thickness measurement in half and add each half to your length and width measurements. Then add another 4 inches for a seam allowance. For instance, if your cushion is 100 inches long, 50 inches wide and 6 inches thick, make the measurements 107 inches long and 57 inches thick. This ensures that the cover fits well without having to add a gusset and provides enough extra fabric for seaming.
Cut two pieces of the fabric, using the measurements you calculated in Step 2.
Wash and dry the fabric to prevent shrinkage and to set the color. Iron the fabric after drying.
Place fabric pieces on top of one another, right sides facing one another. Pin three sides together, leaving one side open.
Sew the three sides together using the sewing machine and a medium-size running stitch. Leave a 2-inch seam allowance. Clip the threads.
Separate the hook-and-loop tape into a hook side and a fastener side. Fold in a 1-inch hem along one open side and pin the hook tape down along the hem. Fold and pin the opposite side and then pin the fastener side to create a closure for your futon cover.
Sew the hook-and-fastener tape into place. Clip excess threads.
Pull your new futon cover onto your futon cushion, like you would place a pillow inside of a pillow case. Fasten the hooks to close and then place the futon onto the frame.