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What Do Blood Pressure Readings Mean?

Posted on August 10, 2017

What is Blood Pressure?

When your heart beats, it pumps blood around your body to give it the energy and oxygen it needs. As the blood moves, it pushes against the sides of the blood vessels. The strength of this pushing is your blood pressure. If your blood pressure is too high, it puts extra strain on your arteries in your brain and heart and other parts of your body, and this may lead to strokes, heart attacks or other serious conditions.

The equipment used for reading blood pressure is known as a sphygmomanometer and it is measured in ‘millimetres of mercury’ (mmHg).  We rarely use mercury blood pressure monitors any longer because of the environmental and health issues of working with mercury but we still use the measurement of mmHg. The measurement can be undertaken with either an old-fashioned model, which is pumped up manually using a bulb on the end of a rubber hose or more commonly these days is the use of a digital device that inflates electronically by pressing a button.

Every blood pressure reading consists of two numbers or levels. They are shown as one number on top of the other. For example, a reading may be 120/80mmHg, and the blood pressure is ‘120 over 80’.

The top number is your Systolic blood pressure. This is the highest pressure when your heart beats and pushes the blood around your body.

The bottom one is your Diastolic blood pressure, which is the lowest pressure when your heart rests between beats.

WHO reports that globally, more than 1 in 5 adults have raised blood pressure – a condition that causes around half of all deaths from stroke and heart disease. Complications from hypertension account for 9.4 million deaths worldwide every year. The good news for high-income countries, such as the UK, widespread diagnosis and treatment with low-cost medication have led to a drop in the number of people with raised blood pressure, as well as the average blood pressure across populations leading to a reduction in deaths from heart disease (2).

Only one of the numbers has to be higher or lower than it should be to count as either high blood pressure or low blood pressure:

90 over 60 (90/60) or less: You may have low blood pressure.

More than 90 over 60 (90/60) and less than 120 over 80 (120/80): Your blood pressure reading is ideal and healthy.

More than 120 over 80 and less than 140 over 90 (120/80—140/90): You have a normal blood pressure reading but it is a little higher than it should be, and you should try to lower it.

140 over 90 (140/90) or higher (over a number of weeks): You may have high blood pressure (hypertension) and should seek medical advice.

The blood pressure classification is published by the World Health Organization (WHO) (2).

Why does my blood pressure fluctuate throughout the day?

A person’s blood pressure can vary throughout the day and the reasons for this might include: having just undertaken strenuous exercise or even standing up for some people; the weather can affect our levels; as can stress, eating, drinking, waking or sleeping.

There is also a “white coat” factor when blood pressure is taken at your GP or Hospital, which might make the result higher than the ones you might take at home. What is most important is the day-to-day changes or longitudinal profile you observe, i.e. is your blood pressure tending towards better or worse values over time?

If in doubt about your blood pressure readings, contact 111 for advice or contact your GP healthcare team.


  1. NHS Choices. Accessed 20/06/17
  2. WHO, World Health Organisation. Accessed 20/06/17


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