Shrinking a wool sweater without having it come out too small is child's play. Allowing it to shrink so that it isn't super stretchy or extra long is all a matter of a little know-how and utilising the proper temperature setting. The easiest way to shrink a wool sweater is by using your washing machine and some careful monitoring.
Place a large brown paper bag under the sweater before you begin washing it. Draw the outline of the sweater on it, to see how large the sweater was before starting and how much shrinkage is desired.
Place the wool sweater in the washing machine with special soap such as Woolite or a lavender soap made for washing more delicate items.
Turn on the machine for the hot/cold setting to shrink the sweater a lot. Turn onto the cold/cold setting to shrink it just a little and make it more of a uniform overall shrinkage.
Wash through the cycle on the desired setting. Stop the machine to look at the wool sweater to make certain it has shrunk to the specifications, and has not shrunk too much.
Agitate the wool sweater in the washing machine to allow it to felt. Do not agitate it too much, so that it doesn't shrink to a child's size. Run the machine on the hot water setting to do this. This will help make the wool become tighter, and softer. This way it won't shrink very much, the wool just comes together.
Place the sweater in the dryer and dry on hot to shrink by a large amount. Place it on a towel for less shrinkage. Arrange the sweater by pulling it to the desired shape, which is called blocking.
Take the original drawing of the sweater while drying it on a towel. Place a piece of clear plastic over the paper bag. Lay the sweater on it to see if it has shrunk enough.
Don't leave the wool sweater in the dryer too long, or it will shrink too much.