What is a normal blood pressure? How to read the numbers

A blood pressure reading such as 128/82 packs two measurements into one line, and whether it counts as normal depends on which guideline you follow. This guide explains the numbers and the categories behind the blood pressure checker and the blood pressure log, so a reading on a home monitor makes sense.

What the two numbers mean

Blood pressure is the force of blood against artery walls, measured in millimetres of mercury (mmHg). The top number, systolic, is the pressure when the heart contracts and pushes blood out. The bottom number, diastolic, is the pressure between beats, when the heart relaxes and refills. A reading of 128/82 means 128 mmHg systolic over 82 diastolic. Both matter: systolic tends to rise with age as arteries stiffen and is the stronger predictor of heart disease and stroke in older adults, while a high diastolic is more common in younger people.

The categories

The 2017 American College of Cardiology and American Heart Association guideline uses these adult categories, with the higher of the two numbers deciding the category:

• Normal: below 120 systolic and below 80 diastolic.
• Elevated: 120 to 129 systolic with diastolic below 80.
• High blood pressure stage 1: 130 to 139 systolic or 80 to 89 diastolic.
• High blood pressure stage 2: 140 or higher systolic or 90 or higher diastolic.
• Severe (hypertensive crisis): above 180 systolic and/or above 120 diastolic.

So 128/82 is stage 1 because the diastolic is in the 80s, even though the systolic alone would only be elevated. A single reading never diagnoses high blood pressure; doctors look at the average of several readings on different days, ideally including home readings. How to measure your blood pressure at home and get accurate readings explains how to take them properly.

How guidelines differ

Not every country draws the lines in the same place. In the UK, NICE diagnoses hypertension at a clinic reading of 140/90 or higher confirmed by home or ambulatory readings averaging 135/85 or higher, and treats 120/80 to 139/89 as normal-to-high-normal rather than as a disease stage. European guidelines also use 140/90 as the main threshold. The American guideline lowered its threshold to 130/80 in 2017 to encourage earlier lifestyle change. The underlying evidence is the same everywhere: risk rises steadily from about 115/75 upwards, so lower is generally better within healthy limits, and the thresholds are policy choices about when to act.

Low blood pressure

Readings below about 90/60 are usually called low (hypotension). For many healthy people, especially young, fit adults, low blood pressure causes no problems and needs no treatment. It matters when it causes symptoms such as dizziness, light-headedness on standing, blurred vision or fainting, or when it drops suddenly, which can be a sign of dehydration, blood loss, infection or a medication effect. Signs of dehydration, and what to do about them covers one of the commonest causes.

Readings that need urgent help

If a reading is above 180/120, rest quietly for five minutes and measure again. If it is still that high, get urgent medical advice the same day. Call emergency services straight away if a very high reading comes with chest pain, shortness of breath, back pain, numbness or weakness, a change in vision, or difficulty speaking, because these can signal damage to organs. For everything else, the useful step is to keep a record: the blood pressure log averages your readings by week and by morning and evening and prints a report for your appointment, and the heart rate zones tool helps if you are starting exercise to bring the numbers down.