If you've purchased a cotton jacket that is just slightly too large for you, you can effectively shrink it down using a few laundering techniques. As long as the material used to make the jacket is 100% cotton, not polyester or acrylic, you can shrink the jacket slightly with the application of heat. This option will spare you the hassle of exchanging the jacket for a smaller size or paying to have it tailored.
Set the temperature of your washing machine to "Hot" and the load size to "Small," then start the wash cycle.
Pour your washing powder into the washer once water starts collecting in the basin.
Place the cotton jacket into the washing machine and wait for the cycle to finish.
Place the washed jacket into your clothes dryer and run it on high heat.
Check the jacket every 10 minutes to see if it has shrunk enough and to prevent it from shrinking too much.
Take the jacket out of the dryer for good once it is the proper size. If necessary, hang it to finish drying.