The size of the appendix that is considered dangerous depends on the context and the diagnostic criteria used. In general, a diameter of 10mm or greater is considered dangerous and may require surgery. However, other studies have shown that a normal appendix can have a maximal outer diameter of up to 12.8mm. The mean maximal diameter of a normal appendix is around 8.19mm. In the context of acute appendicitis, an appendix with a thickness greater than 7mm is generally suggestive of the condition. In a study of patients who underwent laparoscopic appendectomy, those with an appendix diameter of 14mm or greater had a significantly longer postoperative length of stay. It is important to note that the size of the appendix alone is not always a reliable indicator of appendicitis, and other diagnostic criteria should be considered as well.