The average weight for a 5-month-old baby is around 16 pounds for a boy and 14 1/2 pounds for a girl. Typically a baby should double its birth weight by 5 months of age.
An infant may grow one-half to 1 inch a month and gain 5 to 7 ounces a week from birth to 6 months of age. By its first birthday, a baby usually triples its birth weight. Every baby is different; if parents have concerns, they should address them with the child's pediatrician. Doctors tend to be more concerned with a baby's growth curve over time rather than how the child compares to a standard growth chart.