US: XS to Europe Size 58
Cross-market men’s hat and headwear conversion mapping XS specifications into 58.

Analyzing Hat Size Equivalence Across Markets
US: XS: Features a head circumference of 53.5 (21.1 ), measured above the ears where the hat sits comfortably.
Europe Size 58: Features a head circumference of 58.5 (23 ), measured above the ears where the hat sits comfortably.