Things You'll Need
Instructions
Measure the distance from the center of your shoulder to your waist.
Lay the shirt out on a flat surface. Measure this distance from the shoulder down toward the hem on both sides of the neck. Mark these points and use a yardstick to draw a line between them. Turn the shirt over and do the same on the back of the shirt. Connect the front and back lines so the line goes all the way around the shirt at the waist.
Set a sewing machine to sew a straight stitch with a long stitch length. Sew two seams along the top of the shoulders, 1/2 inch apart. Sew from the neck to 1 inch past the shoulder seams.
Pull the bobbin threads on the seams to gather the shirt to fit your shoulders. Adjust the gathers evenly. Set the machine to sew a straight seam with a standard stitch length, and sew between the two rows of gathers to hold them in place.
Thread the machine with upholstery thread that matches the shirt, and set it to sew a wide zigzag stitch with a long stitch length. Sew along the chalk line at the waist of the shirt. If the shirt opens in the front, sew from the inside edge of the placket on one side to the inside edge of the placket on the other side.
Thread a blunt needle with a large eye with thread elastic. Use the needle to thread the elastic through the zigzag seam on the inside of the shirt. The elastic should be 1 inch longer than your waist measurement when it is not stretched. Sew the ends securely in place.