The small intestine is a long, thin tube about 1 inch in diameter and about 20-25 feet long. It is located just below the stomach and takes up most of the space in the abdominal cavity. The entire small intestine is coiled like a hose and the inside surface is full of many ridges and folds. These folds are used to maximize the digestion of food and absorption of nutrients. By the time food leaves the small intestine around 90% of all nutrients have been extracted from the food that entered it.