The High and Low of Checking Blood Pressure

What do the numbers mean? They indicate the risk of health problems

Having your blood pressure checked during a visit to the doctor is as routine as signing in at the front desk. You get a high and a low number. But what do those numbers 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.

Category Systolic (top number)   Diastolic (bottom number)


Less than 120


Less than 80





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

Based on content from the NIH publication, “What Is High Blood Pressure.”

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