• In ready-to-wear, buy garments that fit in the hips and thighs, then extend the waist. This is easier than taking in the hips and thighs. When trying on garments, leave them unbuttoned and unzipped enough so you're comfortable. Measure the gap to determine the extension length (Figure 1).
  

Figure 1
With garment unbuttoned, measure the gap.

• Before purchasing the garment, check to be sure there's enough extra fabric to make the extension, since matching ready-to-wear fabric can be very difficult. Probable places are the hem, pocket facings or waistband facing (Figure 2). On previously sewn garments, raid your scrap bin for matching fabric.
  
  

Figure 3

Sew the extension to the waistband button end.

• Open the hem or facing and cut a fabric piece big enough to make the extension, including seam allowances. Replace the section you removed with lining or other appropriate fabric.
  
  
• Remove the waistband, button and belt loops, marking their positions for easy replacement. To reinforce the extension, attach fusible interfacing to the wrong side. Sew the extension to the button end of the waistband (Figure 3), matching the original width.

• The garment must be let out enough to fit after the extension is added. This can be accomplished at side seams, the center back seam, gathers, pleats, darts or a combination of the above. Many current styles have ample pleats in the front allowing each pleat to be let out up to 1/2" or more without affecting the look. Be sure to add width equally to each side of the center front.
  
  
• After letting out the garment, restitch the waistband, button and belt loops (Figure 4). Press and topstitch as needed.
  

• When a garment fits and falls properly on the body, alterations will be less obvious. If the extension shows when the garment is buttoned, cover it with a belt.
  

Figure 4

Restitch the extended waistband, button and belt loops.