In simple terms
Blood pressure is the force of blood pushing against the walls of your blood vessels as the heart pumps it around the body.
A reading has two numbers, such as 120/80. They are measured in millimeters of mercury, written mmHg, and show the pressure at its highest and lowest points in each heartbeat.
How it works
- Systolic pressure, the first number, is the highest level. It is reached when the heart beats and pushes blood out.
- Diastolic pressure, the second number, is the lowest level. It is reached when the heart relaxes between beats.
It is usually measured with an inflatable cuff wrapped around the upper arm. The cuff tightens for a short time, and a device shows the two numbers. The test takes a couple of minutes.
Where a healthy reading ends depends on the guideline:
- World Health Organization: hypertension is 140/90 mmHg or higher, measured on two different days.
- United Kingdom (NHS): high is 140/90 or higher when checked by a health professional, or 135/85 or higher at home. Low is below 90/60.
- United States (2025 AHA/ACC guideline): normal is below 120/80, and stage 1 hypertension starts at 130/80.
Because thresholds differ, the numbers used to judge a reading can depend on where a person lives.
Why it matters
Pressure that stays too high strains the heart and blood vessels over time and can lead to serious conditions such as stroke and heart disease. High blood pressure usually causes no symptoms, so measuring it is the usual way to find out.
Where you’ll see it
- Checkups at clinics and pharmacies.
- Home blood pressure monitors.
- Health guidelines and public health reports.
Example
A reading of 118/76 mmHg falls within the normal range in the 2025 US guideline.
Often confused with
Heart rate. Heart rate counts how many times the heart beats each minute. Blood pressure measures the force of blood against the vessel walls.
Key facts
- The systolic reading is the pressure in the blood vessels when the heart beats; the diastolic reading is the pressure when the heart rests between beats.1
- WHO diagnoses hypertension when readings on two different days are 140 mmHg systolic or higher and/or 90 mmHg diastolic or higher.1
- The NHS counts 140/90 or higher (checked by a health professional) or 135/85 or higher (checked at home) as high blood pressure.2
- The NHS defines low blood pressure as a reading of less than 90/60 mmHg.3
- The 2025 AHA/ACC guideline defines normal blood pressure as below 120 systolic and below 80 diastolic, and stage 1 hypertension as 130 to 139 systolic or 80 to 89 diastolic.4
This entry explains a medical term. It is not medical advice. If you are concerned about your health, speak with a qualified health professional.
Go deeperWhat Actually Causes High Blood Pressure?Related concepts
In the news
Quick checkIn a reading of 125/82 mmHg, which number is the diastolic pressure?Show answer
82, the second number: the pressure when the heart rests between beats.
Sources
- World Health Organization. Hypertension (fact sheet). 25 September 2025 (accessed 11 September 2026)
- NHS. Blood pressure test. 25 November 2025 (last reviewed) (accessed 11 September 2026)
- NHS. Low blood pressure (hypotension). 11 July 2023 (last reviewed) (accessed 11 September 2026)
- American Heart Association. 2025 High Blood Pressure Guideline: top things to know. 14 August 2025 (accessed 11 September 2026)
Editorially reviewed by Specialty Digest Editorial TeamLast reviewed September 11, 2026Researched and drafted with AI assistanceReport an issue