United Kingdom Size 38–40 to US: S (28–30)

United Kingdom Size 38–40: Corresponds to a waist stretch range of 96.5–101.6 $\text{cm}$ (38–40 $\text{in}$), hip circumference of 111.8 $\text{cm}$ (44 $\text{in}$), thigh clearance of 63 $\text{cm}$ (24.8 $\text{in}$), and fit style Relaxed Boxers & Extended Boxer Briefs.

US: S (28–30): Corresponds to a waist stretch range of 71–76 $\text{cm}$ (28–30 $\text{in}$), hip circumference of 89 $\text{cm}$ (35 $\text{in}$), thigh clearance of 51 $\text{cm}$ (20.1 $\text{in}$), and fit style Briefs, Boxers & Boxer Briefs.