How to understand blood pressure (BP) readings

What does a blood pressure (BP) reading look like?

When you have your blood pressure measured, you will be given two numbers, a top number and a bottom number.

  • Systolic blood pressure. This is the first, or top, number. This is the highest level your blood pressure reaches when your heart beats, forcing blood around your body.
  • Diastolic blood pressure. The second number, or bottom number, is the lowest level your blood pressure reaches as your heart relaxes between beats.

Blood pressure is measured in millimetres of mercury (mmHg). If the first number is 120 and the second number is 80, this would be written as 120/80 mmHg, and you’d call it ‘120 over 80’.

Once you know your numbers, you can use the blood pressure chart to see what they mean and if your blood pressure is in the healthy range. The chart is suitable for adults of any age, as the cut-off point for diagnosing high blood pressure doesn’t change with age.

You can download the chart here: Blood pressure chart

What do the readings mean?

As a general guide:

• 140/90 mmHg or over – you may have high blood pressure
Most doctors use 140/90 mmHg as the cut off for point for diagnosing high blood pressure (hypertension). This is the point where your risk of serious health problems goes up. They might prescribe medications and advise you to make changes to your lifestyle to bring your blood pressure down.

• 120/80 mmHg up to 140/90 mmHg – pre-high blood pressure
Also called high-normal blood pressure. This is not high blood pressure, but it is a little higher than it should be and means you could go on to develop high blood pressure. See how you can make healthy changes to your lifestyle to lower it.

• 90/60 mmHg up to 120/80 mmHg – ideal blood pressure
Also called normal blood pressure. Your blood pressure reading is healthy. At this level you have a much lower risk of heart disease and stroke. Following a healthy lifestyle will help you to keep it in the healthy range.

• 90/60 mmHg or lower – you may have low blood pressure
Low blood pressure usually isn’t a problem, but it can sometimes make you feel faint or dizzy or could be a sign of another health problem.



A single high reading doesn’t necessarily mean you have high blood pressure, as many things can affect your blood pressure throughout the day, such as the temperature, when you last ate, and if you’re feeling stressed.

Your doctor or nurse will probably want to measure your blood pressure a number of times over a few weeks to make sure the reading wasn’t just a one off and that your blood pressure stays high over time.