US: 4–5.5 to United Kingdom Size 5.5–7.5
Cross-market men’s sock conversion mapping 4–5.5 specifications into 5.5–7.5.

Analyzing Sock Size Equivalence Across Markets
US: 4–5.5: 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.
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.