Sometimes, that dress or shirt almost fits – but not quite. You don't want to throw it out, so what do you do? You put in a gusset. A gusset is a piece of material added between the side seams of a garment in order to enlarge it.

A gusset is not difficult to sew, as long as material can be found to match the garment. In general, half a yard (50 centimeters) of material is sufficient for the average gusset. The gusset material should match the original material as closely as possible in order to disguise the alteration.

The first step in making a gusset is to fit the garment and measure how wide the "gap" is between the edges of material. The sewer should then plan to make the gusset on each side half that width, adding a seam allowance. A gusset must be put in on both sides of a garment, if it is to go on the side seams. Some gussets may go in the back seam, in which case only one is needed.

The sewer then cuts two rectangles of the gusset fabric in the proper width and length and sets them aside. He or she then takes the garment, and using a seam ripper, takes out the stitching in the seam where the gusset is to be placed. The sewer should take out enough stitching to fit the gusset comfortably.

For a simple side seam, the sewer then turns the garment inside out, places the gusset material on the seam opening and fits the raw edges together, pinning the gusset to the garment. The gusset material should be facing right side down. The sewer can then pin the gusset in place, marking the beginning and end and the seam allowances.

The gusset should be basted in place into the garment, and then the garment should be fitted again. If the fit is correct, the sewer can stitch the gusset in place, trimming the top and bottom and tapering if necessary. The seam allowances can then be pressed open and trimmed or zig-zag stitched so they will not unravel. By knowing how to add a gusset to a garment, one can help extend the garment's life.