If you find a shirt to be a little too tight in the arms, sew a gusset onto the sleeve. A gusset is a diamond- or triangle-shaped insert sewn onto the underside of a sleeve to expand the armpit. The extra fabric creates room between the upper arm and the body of the shirt, giving you the freedom to move your arms at will without being restricted by the fabric of the shirt. A gusset can be sewn into short and long sleeves.
Insert the tip of a seam ripper into each stitch between the sleeve and body of the shirt. Push the seam ripper through the thread to tear the stitch. Grasp the thread with tweezers and pull the thread out of the shirt. The sleeve will separate from the body of the shirt.
Equip a sewing machine with thread. If you don’t want the stitches to stand out, use thread that is the same color as the fabric.
Turn the sleeve inside out.
Lay the sleeve on a flat surface like a table or counter top with the cuff pointing toward you.
Lay the gusset upside down on top of the top right corner of the sleeve. Align the edges on the right.
Sew the right side of the gusset with the sewing machine to attach it to the sleeve.
Flip over the sleeve so the gusset is underneath.
Fold the sleeve in half lengthwise, from shoulder to cuff. Fold the gusset in half diagonally from the top left to bottom right. The folded fabric should form a 90-degree angle with the seam you previously sewed.
Sew the folds with a sewing machine.
Flip over the sleeve so the gusset is on top.
Unfold the gusset. The edge of the gusset should align with the shoulder of the sleeve.
Sew the last edge with the sewing machine.
Turn the sleeve right side out.
Align the shoulder of the sleeve with the shoulder of the shirt body. The shoulder of the shirt body is now the edge of the gusset.
Sew the open edge of the gusset to the sleeve of the shirt body with a sewing machine.