Some factors that limit the usefulness of any formula relating the two:
1. Brain cells killed while partying in college
2. Differences in your preparation for each exam
3. Differences in the nature of each test
However, I've received several requests recently for information about the relationship between SAT and LSAT scores.
This formula suggests with a moderate degree of certainty (note the qualifying statement here), what your LSAT score might be. I haven't seen any information regarding the origins of this formula, so if you have any, please let me know. This formula is not a prediction or guarantee: simply a suggestion.
LSAT = (SAT Math + SAT Verbal)/20.7 + 100.7
If you studied for 100 hours for the SAT, this formula provides a general guideline for how you might do on the LSAT if you study for 100 hours. Remember to take preparation into account. If you studied for the SAT and got a 1400, but your score prior to studying is only a 150, don't be discouraged. This just means that you have to study.
If you underperformed on the SAT but had a killer GPA in college, this means the LSAT is not likely to accurately predict your performance in law school. If this describes you, I recommend you write an addendum noting this.
For all the visual learners and statistics junkies out there, here's a graph displaying the correlation between SAT and LSAT (using a more complicated equation and a set of only 70 individuals). I found it here. It's far from comprehensive, but I'll share the info and let you decide.