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

Analyzing Hat Size Equivalence Across Markets
US: M: Features a head circumference of 56.5 (22.2 ), 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.