Blood pressure
Pressure in the arteries, given as a systolic and a diastolic value in mmHg
Also known as
Definition
Blood pressure is the force of blood pushing against the walls of the arteries. It is given as two numbers in millimeters of mercury (mmHg): the systolic value (the first, higher number) is the pressure while the heart beats, the diastolic value (the second number) the pressure while the heart rests between beats. A reading of 120/80 mmHg means a systolic value of 120 and a diastolic value of 80. Blood pressure varies with activity, posture, age, caffeine, alcohol, nicotine and medicines.
| Parameter | Value |
|---|---|
| Unit | mmHg |
| Reference Range | Adults: in the US classification (MedlinePlus), readings below 120/80 mmHg are normal and 120–129 mmHg systolic with diastolic below 80 mmHg are elevated. The WHO defines hypertension as a systolic reading of 140 mmHg or higher and/or a diastolic reading of 90 mmHg or higher on two different days. 90/60 mmHg or lower is considered low. Thresholds differ between guidelines; what counts is how your doctor classifies your readings. |
Agree on your personal target range with your doctor.
1 mmHg equals about 0.133 kPa. mmHg is the usual unit for blood pressure in Europe and the US.
↓ What a low value means
Low blood pressure (hypotension) is much less common than high blood pressure and, unlike it, often causes symptoms: dizziness or lightheadedness, nausea, cold, clammy or pale skin, weakness and fainting. Signs of very low blood pressure such as confusion, a weak and rapid pulse or cold skin are an emergency; call your local emergency number. Discuss repeatedly low readings or symptoms with your doctor.
↑ What a high value means
High blood pressure (hypertension) usually causes no symptoms and is often only found by measuring. It raises the risk of heart attack, stroke, and heart and kidney disease. According to the WHO it is linked to older age, genetics, excess weight, physical inactivity, a high-salt diet and alcohol, among other factors. A single high reading is not a diagnosis, because blood pressure fluctuates; nervousness at the doctor's office (white coat effect) can raise it temporarily. Readings above 180/120 mmHg together with chest pain, shortness of breath, numbness, weakness, trouble speaking or vision changes are an emergency; call your local emergency number.
When to test
Measurement is part of a regular checkup; MedlinePlus states at least once a year from age 3, more often with higher risk. For reliable readings, avoid exercise, alcohol, nicotine and caffeine for 30 minutes beforehand, use the bathroom first, sit quietly for about five minutes, feet flat on the floor, arm at heart level. A well-fitting upper-arm cuff and measuring at the same time of day make readings comparable.
Frequently asked questions
What do the two numbers mean? +
The first, higher number is the systolic pressure in the arteries while the heart beats. The second number is the diastolic pressure while the heart rests between beats. Both are given in mmHg, for example 120/80 mmHg.
At what point is it called high blood pressure? +
That depends on the guideline. The WHO sets the threshold at 140/90 mmHg, measured on two different days. The US classification starts stage 1 at 130/80 mmHg, and the European Society of Cardiology introduced a simplified classification with an elevated blood pressure category in 2024. Your doctor makes the diagnosis after repeated measurements.
Why is my reading often higher at the doctor's office than at home? +
Many people are tense when their blood pressure is taken at a practice. This white coat effect can raise blood pressure temporarily. Home readings can add to the picture but do not replace check-ups with your doctor.
Are wrist or finger monitors just as accurate? +
According to MedlinePlus, monitors with an upper-arm cuff are more accurate than those that measure at the wrist or finger. The cuff should also fit snugly and not be too small.
Blood pressure
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.