Europe Size 38–40 to US: 3.5–4.5
Cross-market women’s sock and hosiery conversion mapping 38–40 specifications into 3.5–4.5.

Analyzing Women’s Sock Size Equivalence Across Markets
Europe Size 38–40: Corresponds to a foot length range of 23.5–25 (9.3–9.8 ), US shoe size bracket of 7–9.5, and fit classification Comfort Stretch / Ankle Grip.
US: 3.5–4.5: Corresponds to a foot length range of 20–21.5 (7.9–8.5 ), US shoe size bracket of 3.5–4.5, and fit classification Snug / Petite Fit.