US: XS to United Kingdom Size 7 1/8
Cross-market women’s hat conversion mapping XS specifications into 7 1/8.

Analyzing Hat Size Equivalence Across Markets
US: XS: Features a head circumference of 53 (20.9 ) measured just above the brow and ears.
United Kingdom Size 7 1/8: Features a head circumference of 58.5 (23 ) measured just above the brow and ears.