US: 3XL to United Kingdom Size 18

US: 3XL: Corresponds to a waist/hip size of 100 $\text{cm}$ (40 $\text{in}$), waist range of 91–102 $\text{cm}$ (35.8–40.2 $\text{in}$), total strap length of 110 $\text{cm}$ (43.3 $\text{in}$), and fit classification Expanded / Plus.

United Kingdom Size 18: Corresponds to a waist/hip size of 95 $\text{cm}$ (38 $\text{in}$), waist range of 86–97 $\text{cm}$ (33.9–38.2 $\text{in}$), total strap length of 105 $\text{cm}$ (41.3 $\text{in}$), and fit classification Relaxed Waist / Hip.