An abdominal aorta that is considered normal in size is less than about 3 centimeters, according to the National Institutes of Health. The normal size of the abdominal aorta also varies by sex, age and physical activity level.
With advancing age, the size of the aorta expands approximately 1 to 2 millimeters per year. If the abdominal aorta grows by more than 50 percent of its normal size, however, development of an aneurysm is likely, says the National Institutes of Health.
Tobacco use, family history, atherosclerosis, and being male are risk factors for abdominal aorta aneurysm formation, states Mayo Clinic.