Measure your torso using a cloth tape measure. The three measurements on the NHL's jersey sizing chart are front hem to bottom, back hem to bottom, and chest (armpit to armpit), so these are the measurements that you will need. The hem measurements are the length of the jersey, and the chest measurement is the width. While standing straight, hold one end of the tape measure (starting at 0) at your shoulder line and run the tape down your torso to the point where you would like the hem to hit.
Hold one end of the tape measure at one armpit, and run the tape measure across your chest to the other armpit.
Write each measurement, in inches, on a piece of paper for reference when determining your jersey size.
Use the sizing chart at shop.nhl.com to determine the size that best matches your measurements. Authentic jersey sizes range from 46 to 60.