US: 4-6 to United Kingdom Size 20-22

US: 4-6: Corresponds to a relaxed bust range of 84–88 $\text{cm}$ (33.1–34.6 $\text{in}$), elastic waist range of 66–70 $\text{cm}$ (26–27.6 $\text{in}$), and comfort drape classification Relaxed / Comfort Drape.

United Kingdom Size 20-22: Corresponds to a relaxed bust range of 105–109 $\text{cm}$ (41.3–42.9 $\text{in}$), elastic waist range of 87–92 $\text{cm}$ (34.3–36.2 $\text{in}$), and comfort drape classification Loose Lounge Fit.