United Kingdom Size Large to US: Small / 51mm

United Kingdom Size Large: Corresponds to a nominal width of 57 $\text{mm}$ (2.24 $\text{in}$), length of 200 $\text{mm}$ (7.87 $\text{in}$), average structural girth of 114 $\text{mm}$ (4.49 $\text{in}$), and fit category Large / Roomy.

US: Small / 51mm: Corresponds to a nominal width of 51 $\text{mm}$ (2.01 $\text{in}$), length of 180 $\text{mm}$ (7.09 $\text{in}$), average structural girth of 102 $\text{mm}$ (4.02 $\text{in}$), and fit category Small / Regular-Narrow.