United Kingdom Size 18 to US: XS

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.

US: XS: Corresponds to a waist/hip size of 70 $\text{cm}$ (28 $\text{in}$), waist range of 60–70 $\text{cm}$ (23.6–27.6 $\text{in}$), total strap length of 80 $\text{cm}$ (31.5 $\text{in}$), and fit classification Waist / Snug Cinch.