Blood Pressure

How Blood Pressure is Measured

First, a doctor or other health professional wraps a special cuff around your arm. The cuff has a gauge on it that will read your blood pressure. The doctor then inflates the cuff to squeeze your arm.

After the cuff is inflated, the doctor will slowly let air out. While doing this, he or she will listen to your pulse with a stethoscope and watch the gauge. The gauge uses a scale called “millimeters of mercury” (mmHg) to measure the pressure in your blood vessels.

Another option is to get a blood pressure measurement from the machines available at many pharmacies. There are also home monitoring devices for blood pressure that you can use yourself.

What Blood Pressure Numbers Mean

Blood pressure is measured using two numbers. The first number, called systolic blood pressure, measures the pressure in your blood vessels when your heart beats. The second number, called diastolic blood pressure, measures the pressure in your blood vessels when your heart rests between beats.

If the measurement reads 120 systolic and 80 diastolic, you would say “120 over 80” or write “120/80 mmHg.”

The chart below shows normal, at-risk, and high blood pressure levels. A blood pressure less than 120/80 mmHg is normal. A blood pressure of 140/90 mmHg or more is too high. People with levels in between 120/80 and 140/90 have a condition called prehypertension, which means they are at high risk for high blood pressure.

Blood Pressure Levels
Normal	systolic: less than 120 mmHg diastolic: less than 80mmHg
At risk (prehypertension)	systolic: 120–139 mmHg diastolic: 80–89 mmHg
High	systolic: 140 mmHg or higher diastolic: 90 mmHg or higher