there's not really an exact American equivalent, and you'll find threads debating this very point on these boards, hehe. But generally, a 2:1 as a degree classification would be considered maybe somewhere between a 3.3-3.6 GPA (again, people will disagree on the exact cut off points, but you get the general idea.) I would consider getting a 2:1 on an individual assignment to be about a high B in the American grading system. The grading system starts at Firsts (the highest/best result you can get) and then 2:1 (very good mark) followed by 2:2 (decent, so so) and 3rds (which aren't so good.)