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NIH MedlinePlus the Magazine, Trusted Health Information from the National Institutes of Health

Special Section:
Healthy Blood Pressure

Blood Pressure Numbers: What They Mean

Blood pressure numbers include systolic (sis-TOL-ik) and diastolic (di-a-STOL-ik) pressures. Systolic blood pressure is the pressure when the heart beats while pumping blood. Diastolic blood pressure is the pressure when the heart is at rest between beats.

You will most often see blood pressure numbers written with the systolic number above or before the diastolic, such as 120/80 mmHg. (The mmHg is millimeters of mercury—the units used to measure blood pressure.)

The table below shows normal numbers for adults. It also shows which numbers put you at greater risk for health problems. Blood pressure tends to go up and down, even in people who have normal blood pressure. If your numbers stay above normal most of the time, you're at risk.

Categories for Blood Pressure Levels in Adults

(in mmHg, or millimeters of mercury)


Systolic (top number)


Diastolic (bottom number)

Normal Less than 120 And Less than 80
Prehypertension 120–139 Or 80–89
High blood pressure      
Stage 1 140–159 Or 90–99
Stage 2 160 or higher Or 100 or higher

The ranges in the table apply to most adults (aged 18 and older) who don't have short-term serious illnesses.

All levels above 120/80 mmHg raise your risk, and the risk grows as blood pressure levels rise. "Prehypertension" means you're likely to end up with HBP, unless you take steps to prevent it. —National Heart, Lung, and Blood Institute

Winter 2010 Issue: Volume 5 Number 1 Page 10