The height and weight of a three-month-old baby can be referred to the following standards: First, for boys, the height of a three-month-old boy is about 57-65cm, and the weight is mostly between 5-8kg. If the baby’s weight and height are within the corresponding range, it is basically a normal situation. If the weight and height are significantly lower than the average, look for pathological causes, such as diarrhea or anorexia.