A leather jacket is one of your best protections against the elements, as it creates a strong shield from chilling winds. However, if your leather jacket is too big, it can't insulate your body properly as well as creates a baggy silhouette on your body. While some say it's impossible to shrink leather evenly without ruining it, this is simply not the case. You can shrink leather one size smaller if you approach the project carefully and strategically.
Place a large plastic tub in your bathtub. Fill the plastic tub with lukewarm water until it's at least halfway full. Put on a pair of rubber gloves.
Submerge your leather jacket in the lukewarm water for at least five minutes. You'll see some of the dye start to leak out into the water.
Rub parts of the leather jacket against itself, until you've rubbed the entire surface area of the jacket. This will both rub the dye out into the water and encourage shrinkage. Re-submerge the jacket in the water for 10 minutes.
Wring out as much of the water as you can from the jacket and pat it dry with an old towel. Lay it out to dry on another old towel. Full drying can take two days and requires you to constantly turn the jacket over and switch out fresh, dry towels from under the jacket.
While you can do this procedure directly in your bathtub, the leaking dye might stain it. Once your jacket is dry, wear it with old clothes in case remnants of the dye stain your clothing.