US: M/L to United Kingdom Size 6 7/8
Cross-market women’s hat conversion mapping M/L specifications into 6 7/8.

Analyzing Hat Size Equivalence Across Markets
US: M/L: Features a head circumference of 57.5 (22.6 ) measured just above the brow and ears.
United Kingdom Size 6 7/8: Features a head circumference of 56.5 (22.2 ) measured just above the brow and ears.