Your back length
You may need a friend to help you! Start at the base of the neck and work your way down the spine. Then measure your back to the point where your shirt should be.
These measurements, which you can also compare to the charts here, will tell you your size. You can exchange or return the merchandise if you are not satisfied with the product. You can also order online if you are not sure. There is a big difference between a basketball jersey and a MLB jersey . The styles are different, so your size might differ.
These size charts will help you determine your ideal size.
You can’t go wrong with the huge selection of online options. We Americans all need some sports jerseys in our wardrobes.