The human appendix averages 9 cm in length but can range from 2 to 20 cm. The diameter of the appendix is usually between 7 and 8 mm. The longest appendix ever removed measured 26 cm from a patient in Zagreb, Croatia. The appendix is usually located in the lower right quadrant of the abdomen, near the right hip bone.The base of the appendix is located 2 cm beneath the ileocecal valve that separates the large intestine from the small intestine.he human appendix averages 9 cm in length but can range from 2 to 20 cm. The diameter of the appendix is usually between 7 and 8 mm. The longest appendix ever removed measured 26 cm from a patient in Zagreb, Croatia. The appendix is usually located in the lower right quadrant of the abdomen, near the right hip bone.