US: Medium-Large / 55mm to United Kingdom Size Extra Small

US: Medium-Large / 55mm: Corresponds to a nominal width of 55 $\text{mm}$ (2.17 $\text{in}$), length of 195 $\text{mm}$ (7.68 $\text{in}$), average structural girth of 110 $\text{mm}$ (4.33 $\text{in}$), and fit category Medium-Large / Comfort.

United Kingdom Size Extra Small: Corresponds to a nominal width of 45 $\text{mm}$ (1.77 $\text{in}$), length of 160 $\text{mm}$ (6.3 $\text{in}$), average structural girth of 90 $\text{mm}$ (3.54 $\text{in}$), and fit category Extra Small / Pediatric / Snug.