US: 15.5–18 to United Kingdom Size 5.5–7.5
Cross-market men’s sock conversion mapping 15.5–18 specifications into 5.5–7.5.

Analyzing Sock Size Equivalence Across Markets
US: 15.5–18: 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.
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.