Understanding blood pressure reading and charts
Updated: January 2020
How to measure blood pressure?
Blood pressure is measured in millimetres of mercury, mmHg. It consists of two numbers, such as 130/80, which we say as “130 over 80”. The first is your systolic blood pressure, the maximum pressure your blood attains as your heart beats and pushes it around your body. The second is your diastolic pressure, the minimum level it reaches between beats.
And what’s the definition of high blood pressure?
High blood pressure, also known as hypertension, puts a strain on your heart and blood vessels and makes you more susceptible to heart attacks and strokes.
Normal blood pressure is regarded as being between 120-129 (systolic) and 80-84 (diastolic).
The definition of high blood pressure, according to 2018 ESC/ESH Guidelines, is anything above 140/90 mmHg. If you measure it in the comfort of your own home, where you’re likely to be more relaxed, the limit is slightly lower at 135/85.
If your blood pressure is between 120/80 and 140/90, you may be at risk of developing hypertension at some stage in the future unless you take action to bring it under control. This is called prehypertension.
A blood pressure reading of over 180/120 is dangerously high. Doctors call this a hypertensive crisis, and it requires immediate treatment.
Systolic blood pressure, the top number, is more important than diastolic blood pressure in people over 40. That’s because it’s a better predictor of stroke and heart attack. And only one of the two numbers has to be higher than it should be to count as high blood pressure.
All this can be summarised in a blood pressure chart, like this:
To check your blood pressure against the chart, start from your systolic pressure on the left-hand side, and move your finger to the right until you reach your diastolic pressure. The colour will tell you whether you have normal or abnormal blood pressure.
Tracking blood pressure over time
Bear in mind that a single reading doesn’t tell you very much – you need to take an average of multiple readings, for example morning and evening for a week. Here's how you can track your measurements over time using blood pressure diary (free download) and the 'OMRON connect' app.
Recommended blood pressure monitors
Williams B, Giuseppe M, Spiering W, et al. (2018). 2018 ESC/ESH Guidelines for the management of arterial hypertension. Journal of Hypertension, 36(10). doi: 10.1097/HJH.0000000000001940
Bupa (2018). High blood pressure. Retrieved from www.bupa.co.uk/health-information/heart-blood-circulation/high-blood-pressure-hypertension
Blood Pressure Association (2018). Blood pressure chart. Retrieved from www.bloodpressureuk.org/BloodPressureandyou/Thebasics/Bloodpressurechart