United Kingdom Size 12 to US: XS

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: 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.