Final answer:
An infant's weight usually doubles by six months and triples by one year. Their length may close to double by the end of the first year.
Step-by-step explanation:
Following the initial weight loss right after birth, an infant normally gains an average of about 28 g (1 oz) per day during the first two months. Then, weight gain slows somewhat, and the infant normally gains about 0.45 kg (1 lb) per month during the remainder of the first year. At this rate of weight gain, an infant generally doubles its birth weight by six months after birth and triples its birth weight by 12 months after birth.
Growth in overall body length is also very rapid during infancy, especially in the first few months. Infants normally grow about 2.5 cm (1.0 in.) per month during the first six months. During the second six months, they normally grow about 1.2 cm (0.5 in.) per month. At this rate of growth in length, an infant may close to double its birth length by the end of the first year!