What is a blood pressure reading and what do the two numbers mean?

What is a blood pressure reading and what do the two numbers mean?

Blood pressure numbers differ from person to person. It can sometimes be confusing as the two numbers may seem difficult to understand. Blood pressure is expressed as 131/92, the explanation of the two numbers is as follows:

  • The first number is Systolic Blood Pressure. This refers to the pressure created when the heart beats, pumping blood through the arteries to get to the rest of your body (i.e. where the heart empties blood). The blood being pumped creates a force on your blood vessels, this force is shown in the first number, the systolic number. 

  • The second number is referred to as Diastolic Blood Pressure, as opposed to the systolic reading which is known as the pressure as the heart pumps blood via the arteries, this refers to the pressure in the arteries when your heart is resting (or at rest) between the beats (i.e. when the heart is filling up with blood). This is the period where the heart muscle itself can get oxygen when it fills with blood.

Which number is more important when measuring blood pressure?

While more attention is usually paid to systolic readings, and these are generally regarded as 'more important', both of blood pressure numbers are important, and one should not be prioritised over the other when it comes to measuring overall health.

Blood pressure chart

What blood pressure readings mean

Blood pressure measurements are described as follows1:

    • A healthy adult should have a Systolic pressure that is below 120 mmHg and diastolic below 80 mmHg (i.e. below 120/80)
    • Elevated blood pressure (previously referred to as prehypertension), occurs when blood pressure is higher than normal but not high enough to be diagnosed as hypertension (high blood pressure). The readings for this are as follows – Systolic between 120 to 129 mmHg and diastolic below 80 mmHg.
    • Hypertension, also known as high blood pressure, is diagnosed when the reading is either of the following:
      • Stage 1 hypertension – Systolic between 130 and 139 mmHg or diastolic 80 to 89 mmHg
      • Stage 2 hypertension – Systolic more than 140 mmHg or diastolic more than 90 mmHg
    • Hypotension, also known as low blood pressure is diagnosed when the reading is as follows:
      • Systolic is below 80 mmHg or diastolic is 60 mmHg

An individual is only diagnosed with hypertension (high blood pressure) when they have had three or more persistently elevated blood pressure readings that were taken on separate days when the individual was at rest. 

**My Med Memo - When looking at blood pressure readings, remember that mm Hg means millimetres of mercury, this refers to the units used to measure blood pressure. 


1. American College of Cardiology. 2017. 2017 Guideline for High Blood Pressure in Adults. Available: http://www.acc.org/latest-in-cardiology/ten-points-to-remember/2017/11/09/11/41/2017-guideline-for-high-blood-pressure-in-adults [Accessed 08.01.2019]

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