US: 8.5–10.5 to United Kingdom Size 3.5–5
Cross-market men’s sock conversion mapping 8.5–10.5 specifications into 3.5–5.

Analyzing Sock Size Equivalence Across Markets
US: 8.5–10.5: Corresponds to a US shoe size range of 8.5–10.5, foot length of 26.5–28 (10.4–11 ), and fit classification Standard Regular Fit.
United Kingdom Size 3.5–5: Corresponds to a US shoe size range of 4–5.5, foot length of 22–23.5 (8.7–9.3 ), and fit classification Snug / Compact Fit.