Healthcare providers measure blood pressure with an instrument called a blood pressure monitor, or sphygmomanometer . The monitor includes a cuff, a pump with a valve, and a gauge. This is how the process occurs:

  • Your healthcare provider wraps the cuff around your upper arm. The provider will make sure that the cuff is the right size for your arm. Small cuffs are available for children. Some adults may need an extra large cuff.
  • Then the provider inflates the cuff by closing the valve and squeezing a small pump. This stops the flow of blood to your arm for a few seconds.
  • Your provider places the end of a stethoscope on the inner surface of your elbow.
  • Your provider opens the valve to slowly release air from the cuff. As your blood begins to flow back through your arm it makes a pulsing sound. Your provider listens with a stethoscope for this sound.
  • When the first sound of the pulse is heard, the provider records the number from the pressure gauge. This is your systolic blood pressure. It represents the pressure in your arteries when your heart beats or contracts.
  • Then when the sound fades or disappears, your provider records that number from the pressure gauge. This is your diastolic blood pressure. It represents the pressure of the blood in your arteries when your heart rests between beats.
  • Your provider will write your blood pressure as a fraction. The top number is your systolic blood pressure. The bottom number is your diastolic blood pressure. For instance, a systolic pressure of 130 and a diastolic pressure of 75 is written as 130/75 and read as 130 over 75. Blood pressure is measured in millimeters of mercury, shown as mm Hg.
  • Your healthcare provider will probably take at least two readings separated by 2 minutes. Your doctor will then average the readings.

How do the numbers show what's happening in my heart?

The top number, or systolic pressure, is the measurement of the pressure of the blood in your arteries when your heart contracts, or beats, and is forcing blood out to the rest of your body. The bottom number, or diastolic pressure, is the measurement of pressure of the blood in your arteries when your heart is relaxing between beats. This is when your heart is filling for the next beat. To learn more, see What Do the Numbers Mean?