United Kingdom Size 50 to US: 28

United Kingdom Size 50: Corresponds to a waist size of 125 $\text{cm}$ (50 $\text{in}$), total strap length of 140 $\text{cm}$ (55.1 $\text{in}$), and recommended fit classification Extended / Plus.

US: 28: Corresponds to a waist size of 70 $\text{cm}$ (28 $\text{in}$), total strap length of 85 $\text{cm}$ (33.5 $\text{in}$), and recommended fit classification Snug / Tailored.