I bought these for my guy, as he LOVES these briefs and traveled to Europe with them.
I went to the site and looked up what his size would be and a medium was recommended for his waist size.
While the ExOfficio boxer briefs are GREAT to travel with (dry quickly as advertised), material is comfortable, etc.
The sizing seemed to be off. My guy, who is lean, felt that the medium was pretty snug on his waist. He wears a 33 in his jeans. If ordered again, I will order the large for him. Might just be a matter of personal comfort.