Measuring 101: How to Measure Shoulder Width
This measurement is taken from one end of the shoulders to the other.
If you’re measuring your friend have him look forward with relaxed shoulders in natural stance. Start measuring from one end of the shoulder
(at the shoulder seam of shirt) to the other end or seam of the shirt. Averages – S: Between 16-17″ M: Between 18-19″ L: Between 20-21″