First, understand that the score you receive from an intelligence test is only an estimation of your intelligence. Intelligence tests are not standardized which means the score you receive will vary from test to test.
Take an IQ test. There are a number of free tests available online. Mensa International, one of largest and oldest high IQ societies in the world, offers an intelligence test as well as important information regarding becoming a member of their high IQ society.
Understand your score. For example, an IQ score between 91-110 represents a normal level of intellect. A score between 121-150 represents very high intelligence. Any score above 170 means you are a genius. In order to be eligible to join Mensa International, you must score a 130.
Take a second intelligence test. The validity and reliability of some online intelligence tests come into question because some of these tests do not adhere to the guidelines of standardized intelligence tests. Upon completion, compare the results from each test to help you gain a better approximation of your score.