United Kingdom Size 18 to US: S

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: S: Corresponds to a waist/hip size of 75 $\text{cm}$ (30 $\text{in}$), waist range of 66–76 $\text{cm}$ (26–29.9 $\text{in}$), total strap length of 85 $\text{cm}$ (33.5 $\text{in}$), and fit classification Standard Waist / Hip.