It depends on which schools you are looking at, as they all use a different scale. For example, the University of Texas just takes LSAT + 15*GPA which tends to lead to some big numbers. If you see someone with a large score, try plugging in your numbers for the same school; chances are you will have a number also in that range. In order to get the specific formulas, go to the LSAC and login in to LSDAS. Click "Account Status -> Transcript -> Admission Index".

Most schools only use the formula as a rough ranking guide. I have however read, though I don't know if it's true, that some schools look at the 1L grades and compare them to the applications. They then find a formula that would have allowed them to predict that first-year GPA based off the student's UGPA and LSAT scores, and that is the formula they use for next year's admissions cylce.