This is a method of estimating your class rank based off of various data points. Linked below is an online calculator that should be fairly intuitive to use, and I have also left formulas behind which can be plugged into Excel (in case the calculator goes down).
Estimator mechanics:This is an estimate based off the assumption that your school's GPA distribution is roughly "normal" ("normal" distributions being a specific, common type of distribution whose characteristics are likely to match your school's grade distribution). The estimator utilizes two data points to figure out what your school's grade distribution looks like, and then uses that estimate of your school's grade distribution to tell you where you rank, based upon your GPA.
The first data point the estimator needs can be any ranked data point (e.g. 3.5 is top 25%, or 3.1 is bottom 25%). The second data point the estimator needs is the median GPA (if you don't have the median GPA, the mean should be pretty much the same number, assuming your school has a normal distribution).
I should stress that this will yield only an estimate, though I think it should be fairly accurate (unless you're an outlier of sorts, either high or low. It is likely to be less accurate for outliers).
Online Calculator, graciously made by LSATSCORES2012http://mylsn.info/class_rank.phpExcel code:Open excel and follow these directions:
Cell A1: enter your GPA
Cell A2: enter the median gpa at your school.
Cell A3: enter the GPA of a certain ranked data point (e.g. 3.7 is ~ top 6.8% at UVA, so someone from UVA would enter 3.7)
Cell A4: enter the rank of that GPA (e.g. enter 6.8 if you're at UVA).
Cell A5: copy and paste this formula:
=(1 - NORMDIST(A1, A2, (A3 - A2)/NORMSINV(1-(A4/100)), TRUE))*100
Press enter. Whatever comes up in A5, you're in the top that percentile. You can save the sheet and use it later, as well.
The majority of the replies below are people I estimated for using the manual workaround, until we figured out a way to just put the calculator online. After that there's a little discussion about the calculator and various requests for estimation.