The normal height of a twelve-year-old girl should be around 1.54 meters and her weight is usually around 32kg. There is a formula for calculating height and weight in this period, and you can assess for yourself whether the height and weight are in the normal range according to the formula. Standard height (cm) should = age x +70. weight kg = age x 2 + 8. Twelve-year-old girls female characteristics have begun to develop, parents are advised to pay attention to good physiological hygiene guidance, the first menstruation, pay attention to hygiene, do not eat cold spicy stimulating food during menstruation.