Definition of IQ : What is IQ? IQ (intelligence quotient) = (Mental Age / Chronological Age) x 100. The IQ of a child between the ages of 5 to 16 years old is calculated by dividing the child's mental age by his chronological age and then multiplying the result by 100. If a 10 year old child performs mentally at a 10 year old level, the IQ is calculated as 10 divided by 10 equaling 1, and multiplying the 1 by 100 equals an IQ of 100. If the 10 year old child mentally performs at a 20 year old level, then 20 over 10 equals 2, and multiplying 2 by 100 equals an IQ score of 200. Adult IQ is calculated by supervised IQ testing. Adult IQ scores are specific to each IQ test and are not interchangeable between one IQ test and another. Membership qualifications to most high IQ societies require percentile ratings instead of IQ scores. The IQ formula (MA/CA) x 100 = IQ was created as an indicator, not based on mathematical rules. The formula could have been (MA/CA)x10 or (MA/CA)x1000. IQ scores are relative numbers, of no real measurement other than to show relative differences of measurable mental performance between different people taking similar tests. by sandeep