United Kingdom Size 18 to US: L

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: L: Corresponds to a waist/hip size of 85 $\text{cm}$ (34 $\text{in}$), waist range of 76–86 $\text{cm}$ (29.9–33.9 $\text{in}$), total strap length of 95 $\text{cm}$ (37.4 $\text{in}$), and fit classification Standard Waist / Hip.