The average 6-month-old baby boy weighs between 16 and 19 pounds while 6-month-old baby girls weigh between 15 and 18.5 pounds. These numbers are based on weights between the 25th and 75th percentiles.
Babies gain approximately 1.5 to 2 pounds a month during their first six months of life. By 6 months of age, growth slows to about a pound each month. Babies tend to at least double their weight by the time they are 6 months old. For babies who were born prematurely, it is best to look at weight charts based on the baby's gestational age, which means the baby's age based on due date not actual birth date.