You will need to have your undergraduate institution (in my case Newcastle University) send a copy of your transcript to a place such as World Education Services, who will "translate" it into the 4.0 scale.
I did very well on the LSAT but I was unpleasantly surprised by my GPA conversion. I got a very solid 2.1 (and Newcastle is a good university) but it was converted to a 3.3 GPA, which is really very average. I know that at Newcastle they wouldn't allow US students to start a degree without first doing a "foundation year" so my understanding has always been that a UK degree is considered to be harder than its American equivalent. I got it to my law school of choice, anyway.
May I ask why you are going to law school out here? I am married to an American, which is why I am here.