The table presented here shows the classification of blood pressure adopted by the American Heart Association for adults who are 18 years and older. It assumes the values are a result of averaging resting blood pressure readings measured at two or more visits to the doctor.

In the UK, clinic blood pressures are usually categorized into three groups; low (90/60 or lower), normal (between 90/60 and 139/89), and high (140/90 or higher).

Blood pressure fluctuates from minute to minute and normally shows a circadian rhythm over a 24-hour period, with highest readings in the early morning and evenings and lowest readings at night. Loss of the normal fall in blood pressure at night is associated with a greater future risk of cardiovascular disease and there is evidence that night-time blood pressure is a stronger predictor of cardiovascular events than day-time blood pressure.

Various factors, such as age and sex, influence a person's blood pressure and variations in it. In children, the normal ranges are lower than for adults and depend on height.Reference blood pressure values have been developed for children in different countries, based on the distribution of blood pressure in children of these countries. As adults age, systolic pressure tends to rise and diastolic tends to fall. In the elderly, systolic blood pressure tends to be above the normal adult range, thought to be largely because of reduced flexibility of the arteries. Also, an individual's blood pressure varies with exercise, emotional reactions, sleep, digestion and time of day (circadian rhythm).

Differences between left and right arm blood pressure measurements tend to be random and average to nearly zero if enough measurements are taken. However, in a small percentage of cases there is a consistent difference greater than 10 mm Hg which may need further investigation, e.g. for obstructive arterial disease.

The risk of cardiovascular disease increases progressively above 115/75 mm Hg. In the past, hypertension was only diagnosed if secondary signs of high arterial pressure were present, along with a prolonged high systolic pressure reading over several visits. Regarding hypotension, in practice blood pressure is considered too low only if noticeable symptoms are present.

Clinical trials demonstrate that people who maintain arterial pressures at the low end of these pressure ranges have much better long term cardiovascular health. The principal medical debate concerns the aggressiveness and relative value of methods used to lower pressures into this range for those who do not maintain such pressure on their own. Elevations, more commonly seen in older people, though often considered normal, are associated with increased morbidity and mortality.With the Quantum Resonance Magnetic Analyzer know the Blood pressure better.