Shrinking is usually something most people seek to avoid, but for people looking to create a tight, form-fitting look, sometimes buying a sweater that is a decent fit and then shrinking it at home is a good option. Following these steps will shrink any cotton sweater down a notch.
Buy a cotton sweater that is not pre-shrunk or pre-washed. While any cotton garment will shrink at least a little as a result of this process, a garment that has not been previously shrunk will shrink a lot.
Set your washing machine to its highest hot-water setting and for the longest duration, and wash the cotton sweater.
Put the sweater in the dryer, set that for the highest heat setting, and dry it. Then leave it in the dryer for a while.