What is considered low blood pressure?

Depends on symptoms: This varies by age and symptoms. One important point is that a blood pressure that others consider normal /good (such as 110/70) could actually be too low in some medical conditions such as aortic stenosis. Generally, 90/60 would be a good official answer as the bottom limit, but this is normal in conditioned athletes and kids. Fatigue, dizziness, fainting are signs pressure may be too low.

Just a number: Well 120/80 has been considered average. Under 100 is getting low. But what is more important is how do you feel. If you feel well, i would not worry about a low blood pressure. Actually people with a low blood pressure live longer. I have seen patients with a pressure of 80/60 who feel quite well.