US: XS to Europe Size 56
Cross-market men’s hat and headwear conversion mapping XS specifications into 56.

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 56: Features a head circumference of 56.5 (22.2 ), measured above the ears where the hat sits comfortably.