It can be very frustrating to discover that a new pair of jeans is just a bit too loose. Fortunately, there are a few things you can do to try shrinking your stretch jeans. Although some high-quality and designer jeans are pre-shrunk and therefore don't respond well to attempts at shrinking, many jeans will shrink as much as 1/4 inch after washing and drying the first time. Keep in mind that most jeans will stretch a bit with wear and shrink again each time they are washed.
Wash the jeans by themselves in a hot water setting. Add 1/2 cup of ammonia to prevent the color from fading, unless you don't mind if the jeans fade a little.
Put the jeans in the dryer without any other clothing. Use the hottest setting and let the dryer continue to run for about fifteen minutes after the jeans are dry.
Repeat the wash and dry process, again using the hottest settings.
If your jeans still have not shrunk enough, try filling a bathtub with the hottest water you can stand. Put the jeans on and sit in the bathtub for about thirty minutes. This process causes jeans not only to shrink but also to conform to your body shape, providing a custom fit. Afterward, take the jeans off and allow them to dry flat (do not use a dryer).