United Kingdom Size 31–33 to US: XL (38–40)

United Kingdom Size 31–33: Corresponds to a waist stretch range of 78.7–83.8 $\text{cm}$ (31–33 $\text{in}$), hip circumference of 96.5 $\text{cm}$ (38 $\text{in}$), thigh clearance of 55 $\text{cm}$ (21.7 $\text{in}$), and fit style Briefs, Boxers & Boxer Briefs.

US: XL (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.