US: 54-56 to United Kingdom Size 42-44
Cross-market men’s sleepwear conversion mapping 54-56 specifications into 42-44 for lounge pants, pajama sets, and robes.

Analyzing Sleepwear Size Equivalence Across Markets
US: 54-56: Corresponds to a relaxed chest range of 130–134 (51.2–52.8 ), elastic waist range of 116–122 (45.7–48 ), and fit classification Loose Lounge Fit.
United Kingdom Size 42-44: Corresponds to a relaxed chest range of 106–110 (41.7–43.3 ), elastic waist range of 92–98 (36.2–38.6 ), and fit classification Relaxed / Comfort Fit.