US: 13.5–15 to United Kingdom Size 3.5–5
Cross-market men’s sock conversion mapping 13.5–15 specifications into 3.5–5.

Analyzing Sock Size Equivalence Across Markets
US: 13.5–15: Corresponds to a US shoe size range of 13.5–15, foot length of 30.5–32 (12–12.6 ), and fit classification Extended Volume / High Stretch.
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.