A false hem, or hem facing, is a smart solution when you do not have enough fabric to create a regular hem. One reason for using false hems is to save on the cost of fabric. Historically, dressmakers would often use a less expensive fabric for the hem, which no one would see anyway. Creating a false hem in your trousers may take a bit of extra time, but no one will be able to tell the difference.
Cut the extra fabric into a rectangular shape, about 4 inches wide and slightly longer than the circumference of your pant leg. You will need two pieces this size.
Pin the rectangle of extra fabric to the bottom of the trousers, with the outsides of the fabric facing together. The trousers should be right side out, with the inside of the extra fabric showing.
Sew the fabric together, starting from the inner seam and going around the pant leg. Stop sewing when you have come around to the other end.
Close the opening on the extra fabric by sewing the pieces together, with the right sides of the fabric facing each other. Trim any excess fabric.
Iron the fabric straight down. At this point, you should be able to see the extra fabric at the end of the pant leg.
Roll the bottom edge of the extra fabric in twice. Sew along this line to create a small hem. Turn the trousers inside out.
Fold the extra fabric up to create the hem in the pant leg. Pin the hem in place. Iron the hem flat.
Sew the hem of the trousers by hand using a basting stitch. Repeat all of the steps to create a false hem in the other pant leg.
Many sewing machines allow you to remove a piece of the machine, just in front of the needle, to create sleeves. Remove this attachment when working with trousers, and slip the whole leg around the sewing machine.