United Kingdom Size 40 to US: 30

United Kingdom Size 40: Corresponds to a waist size of 100 $\text{cm}$ (40 $\text{in}$), total strap length of 115 $\text{cm}$ (45.3 $\text{in}$), and recommended fit classification Relaxed / Comfortable.

US: 30: Corresponds to a waist size of 75 $\text{cm}$ (30 $\text{in}$), total strap length of 90 $\text{cm}$ (35.4 $\text{in}$), and recommended fit classification Standard / Regular.