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

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: Features a head circumference of 57.5 (22.6 ) measured just above the brow and ears.