US: 11–13 to United Kingdom Size 15–17.5
Cross-market men’s sock conversion mapping 11–13 specifications into 15–17.5.

Analyzing Sock Size Equivalence Across Markets
US: 11–13: Corresponds to a US shoe size range of 11–13, foot length of 28.5–30 (11.2–11.8 ), and fit classification Relaxed / Comfort Stretch.
United Kingdom Size 15–17.5: Corresponds to a US shoe size range of 15.5–18, foot length of 32.5–35 (12.8–13.8 ), and fit classification Max Volume / Bariatric & Therapeutic.