Based upon our experience:
Woman: 71% Small - 26% Medium - 3% Large
Man: 23% Small - 59% Medium - 18% Large
Get a tailor’s tape measure and put it tightly around your wrist and check what your size is.
Your wrist measures from 15 to 16,5cm: Small
Your wrist measures from 16,5 to 18,5cm: Medium
Your wrist measures from 18,5 to 20cm: Large