The short answer
The top number, systolic pressure, is the pressure while the heart contracts; the bottom number, diastolic pressure, is the pressure between beats. Under current American Heart Association categories, normal is below 120/80 mmHg, elevated is 120 to 129 systolic with diastolic below 80, stage 1 hypertension is 130 to 139 or 80 to 89, and stage 2 is 140 or higher or 90 or higher. Diagnosis is based on repeated readings taken properly, not on a single measurement.
Blood pressure is cheap to measure and easy to measure badly. Technique, timing, posture and even conversation change the result by amounts that can move a reading between categories, which is why understanding the measurement matters as much as understanding the numbers.
Key takeaways
- Systolic is the pressure during contraction; diastolic is the pressure between beats.
- Normal is below 120/80 mmHg, with stage 1 hypertension starting at 130 or 80.
- Technique changes results: sit still, support the arm, do not talk, average multiple readings.
- Diagnosis relies on repeated readings, often including measurements outside the clinic.
- Readings above 180/120 mmHg need immediate attention.
What the two numbers describe
Systolic pressure is the peak pressure in the arteries as the heart contracts. Diastolic pressure is the pressure remaining while the heart relaxes and refills. Both are reported in millimetres of mercury.
Blood pressure varies constantly through the day, rising with activity, stress and caffeine, and falling during sleep. A single value is a snapshot of one moment under one set of conditions.
Arterial stiffness tends to increase with age, which is one reason systolic pressure commonly drifts upward from midlife onward.
Categories used in the United States
These thresholds come from the American Heart Association and American College of Cardiology guideline. Categories inform conversations; they do not diagnose you from one reading.
| Category | Systolic (mmHg) | Diastolic (mmHg) | |
|---|---|---|---|
| Normal | Less than 120 | and | Less than 80 |
| Elevated | 120 to 129 | and | Less than 80 |
| Hypertension stage 1 | 130 to 139 | or | 80 to 89 |
| Hypertension stage 2 | 140 or higher | or | 90 or higher |
| Hypertensive crisis | Higher than 180 | and/or | Higher than 120, seek immediate care |
Measuring properly at home
Home readings often represent your usual pressure better than a single clinic measurement, provided the technique is right. A validated upper-arm cuff with the correct size is the starting point.
- Avoid caffeine, exercise and smoking for 30 minutes beforehand.
- Empty your bladder first.
- Sit quietly for five minutes with your back supported.
- Keep both feet flat on the floor and legs uncrossed.
- Rest the cuffed arm on a table at heart height, cuff on bare skin.
- Do not talk during the measurement.
- Take two or three readings a minute apart and record the average.
- Measure at the same times each day, typically morning and evening, for at least a week.
Why context changes interpretation
White coat hypertension describes readings that are high in a clinic and normal elsewhere. Masked hypertension is the opposite, and is arguably more concerning because it goes unnoticed. Both are reasons home or ambulatory monitoring is often requested before treatment decisions.
Treatment targets also vary with age, kidney function, diabetes, previous cardiovascular events and how well a person tolerates medication. That is why two men with identical readings can be given different plans.
Commonly confused
“You can feel high blood pressure.”
Hypertension is usually symptom-free, which is why it is measured rather than sensed. Headaches and nosebleeds are not reliable indicators.
“One high reading means hypertension.”
Diagnosis rests on repeated properly taken readings, usually including measurements outside the clinic.
“Once readings are normal on medication, treatment can stop.”
Normal readings usually reflect the treatment working. Stopping or changing medication is a decision to make with the prescribing clinician.
Questions to raise with a healthcare professional
- Should I confirm these readings with home or ambulatory monitoring?
- Is my cuff the right size and a validated device?
- What is my target given my age and other conditions?
- Could any medication or supplement I take be raising my blood pressure?
- Should we look for causes such as sleep apnea or kidney disease?
When to seek care
Worth a routine appointment
- Home readings consistently at or above 130/80 mmHg over a week.
- Readings that remain high despite treatment.
Seek help without delay
- A reading higher than 180 systolic or 120 diastolic: rest five minutes and repeat, and if it remains that high contact medical care immediately.
- Very high readings with chest pain, breathlessness, back pain, weakness, difficulty speaking or visual change. Call 911 in the United States.
References
- American Heart Association. Understanding blood pressure readings
- Centers for Disease Control and Prevention. Measure your blood pressure
- National Heart, Lung, and Blood Institute. High blood pressure: causes, diagnosis and treatment
How this article is reviewed
Aldrick articles are written from published guidance and peer-reviewed research, checked against our evidence standards and re-reviewed when guidance changes. Spotted something inaccurate or out of date? Tell us and we will correct it and update the review date.
This article is educational. It does not diagnose conditions or replace evaluation by a qualified clinician.