Final answer:
By 12 months, an infant's weight usually triples from birth, and their height increases by about 25 centimeters (10 inches) from the average birth length of 19.5 inches.
Step-by-step explanation:
By 12 months, an infant's weight typically triples from birth. So, if a baby weighs about 12 pounds when born, the expected weight by the first year would be approximately 36 pounds. However, the actual increase may vary, with a normal range being between 20 and 40 pounds at two years of age. Regarding height, a newborn's length usually increases by about 25 centimeters (10 inches) in the first year, from an average of 19.5 inches to about 29.5 inches by 12 months.