Blood Pressure Home > Blood Pressure Reading

When reading blood pressure, the number is written like a fraction. The top number measures the systolic blood pressure (when the heart is beating); the bottom number represents diastolic blood pressure (when the heart is at rest). When several readings are taken over a few days, your average blood pressure can be determined.

Blood Pressure Reading: An Overview

The two numbers that measure your blood pressure are written like a fraction: one number on top and one on the bottom (128/82). The number on top represents systolic pressure. Systolic blood pressure measures the pressure inside your blood vessels at the moment your heart beats. The number on the bottom refers to your diastolic pressure. Diastolic blood pressure measures the pressure in your blood vessels between heartbeats, when your heart is resting.
Blood pressure changes frequently throughout the day, so it is better to use more than one reading to figure out your average blood pressure. This is because, from day to day, a person's blood pressure readings usually fluctuate within a certain range. Posture, exercise, tension, and nicotine use are a few things that can make a person's blood pressure change within a few minutes.
When comparing your blood pressure to what's thought of as "normal," it is important to consider your:
  • Overall health
  • Diet
  • Family history
  • Lifestyle.

When Reading Blood Pressure, What's Too High?

To determine your average blood pressure reading, you will need to have your blood pressure taken two or more times, with each reading recorded on a different day. Generally, anything under 120/80 is considered normal blood pressure, but extremely low blood pressure can also be a problem. If you have an average blood pressure between 120/80 and 139/89, this is known as "prehypertension." If your average blood pressure is over 140/90, you have high blood pressure.
A single blood pressure reading of more than 140/90 doesn't necessarily mean that you have high blood pressure. It is likely that your doctor will want to monitor your blood pressure over a period of time to see if it stays there. You can also have high blood pressure if the average of only one of the numbers in your reading is too high (see Isolated Systolic Hypertension).
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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