Many people define normal blood pressure as an average reading of 120/80 or below. However, normal blood pressure can actually fall anywhere in a range from 90/60 to 120/80 -- it's not just one set number. An average blood pressure can only be determined when multiple readings are taken over at least three days. Measuring blood pressure often involves wrapping a fabric cuff around the arm and then slightly inflating it. Blood pressure changes frequently throughout the day. Posture, nicotine use, and level of exercise are a few of the things that can make blood pressure change within a few minutes. Several things (such as lifestyle and family history) can affect a person's normal blood pressure range. Be mindful of this when comparing your blood pressure to what's considered "normal blood pressure."