IQ is the ratio of mental age to chronological age. It is generally expressed by the formula: IQ = (mental age/chronological age) × 100. Usually people regard IQ 100 as the standard line for normal children's IQ. Children with IQ between 90 and 129 are considered normal children. Children with IQ above 130 (some people think it is above 140) are considered supernormal children. Children with IQ below 89 are considered to have low intelligence. Children with IQ Those below 70 are mentally retarded.