According to the Stanford Revision of the Binet-Simon Scale of Intelligence, the average IQ score is between 90 and 109, so an IQ of 110 or higher signifies above-average intelligence. Genius level IQ begins between scores of 140 to 145.
Only 1/4 to 1 percent of test takers score 140 or higher. The highest genius level is a score between 180 and 200. Any score below 70 indicates a mental handicap, with varying degrees depending on the score. An IQ under 20 is considered profound mental retardation, and only 1 percent of those who score below a 70 are in this range.