US: 11–13 to United Kingdom Size 5.5–7.5
Cross-market men’s sock conversion mapping 11–13 specifications into 5.5–7.5.

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 5.5–7.5: Corresponds to a US shoe size range of 6–8, foot length of 24–26 (9.4–10.2 ), and fit classification Standard Athletic / Form Fit.