United Kingdom Size 20 to US: M

United Kingdom Size 20: Corresponds to a waist/hip size of 100 $\text{cm}$ (40 $\text{in}$), waist range of 91–102 $\text{cm}$ (35.8–40.2 $\text{in}$), total strap length of 110 $\text{cm}$ (43.3 $\text{in}$), and fit classification Expanded / Plus.

US: M: 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.