US: M/L to Europe Size 53
Cross-market men’s hat and headwear conversion mapping M/L specifications into 53.

Analyzing Hat Size Equivalence Across Markets
US: M/L: Features a head circumference of 57.5 (22.6 ), measured above the ears where the hat sits comfortably.
Europe Size 53: Features a head circumference of 53.5 (21.1 ), measured above the ears where the hat sits comfortably.