Small intestine
It is approximately 1.5 cm in diameter in newborns after 35 weeks of gestational age, and 2.5–3 cm (1 inch) in diameter in adults. On abdominal X-rays, the small intestine is considered to be abnormally dilated when the diameter exceeds 3 cm. On CT scans, a diameter of over 2.5 cm is considered abnormally dilated. The surface area of the human small intestinal mucosa, due to enlargement caused by folds, villi and microvilli, averages 30 square meters.
Stomach
In adult humans, the stomach has a relaxed, near empty volume of about 75 millilitres. Because it is a organ, it normally expands to hold about one litre of food. The stomach of a newborn human baby will only be able to retain about 30 millilitres.