First, calculate your raw score. This can be done simply by adding the score of each individual section.
Locate a table showing all critical data for the version of the LSAT you took. If you used an official LSAT book, this information will be in the back of your LSAT prep book. These data should include charts that show which raw scores are equal to which LSAT scores.
Use the chart to determine your LSAT score. This score is based on your performance relative to individuals who actually took the test.