The normal body size of a three-month-old baby is related to gender, heredity, feeding and illness, and is usually about 60cm in height and 6kg in weight. 1. Gender. Male babies are 55.3cm-69.0cm in height and weigh 4.69kg-9.37kg; female babies are 54.2cm-67.5cm in height and 4.40kg-8.71kg in weight. there are individual differences. 2. Genetic. The normal size of a three-month-old baby is also related to the height of the parents. 3. Feeding. In addition to the influence of gender and genetic factors, post-birth feeding is also very important. Insufficient feeding and poor growth and development in the early days will also affect the future growth of height and weight. 4. Disease. It is also necessary to avoid cold and cross-infection, avoid illness, in order to prevent disease caused by slow growth and development of the baby. It is recommended to go to the Children’s Health Department for regular medical checkups, once found that the baby’s height development is abnormal, timely intervention is needed.