United Kingdom Size 12 to US: S

United Kingdom Size 12: Corresponds to a waist/hip size of 80 $\text{cm}$ (32 $\text{in}$), waist range of 71–81 $\text{cm}$ (28–31.9 $\text{in}$), total strap length of 90 $\text{cm}$ (35.4 $\text{in}$), and fit classification Standard 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.