Know when to seek emergency help
Call 911 or your local emergency number for symptoms that may indicate a heart attack or stroke, such as chest pain, severe shortness of breath, new weakness, or trouble speaking. Do not wait for a calculator or another blood-pressure reading.
For a reading higher than 180 systolic and/or higher than 120 diastolic without concerning symptoms, the American Heart Association advises waiting at least one minute, repeating the measurement, and contacting a healthcare professional if it remains very high. A very high reading with concerning symptoms is an emergency. [1]
Pregnancy and the postpartum period require pregnancy-specific assessment; the adult table below should not be used to delay contacting the maternity care team about symptoms or elevated readings.
What the two numbers mean
Systolic pressure is the upper number and describes pressure when the heart contracts. Diastolic pressure is the lower number and describes pressure between beats. The unit is millimeters of mercury, written mm Hg.
A result of 128/78 means a systolic pressure of 128 and a diastolic pressure of 78. It is not a fraction to divide, and averaging the two numbers does not produce the category used in routine blood-pressure guidance.
U.S. adult categories from the American Heart Association
| Category | Systolic | Diastolic |
|---|---|---|
| Normal | Below 120 | And below 80 |
| Elevated | 120–129 | And below 80 |
| Stage 1 hypertension range | 130–139 | Or 80–89 |
| Stage 2 hypertension range | 140 or higher | Or 90 or higher |
| Severe range requiring prompt attention | Higher than 180 | And/or higher than 120 |
When the two values fall in different categories, the higher category governs this screening classification. A single reading in a category is not, by itself, a diagnosis or a medication instruction. [1]
Other countries or clinical contexts may use different thresholds. Use the guidance relevant to the person and care setting.
Make the measurement interpretable
Use an appropriate cuff and follow the monitor manufacturer’s and clinician’s instructions. Body position, cuff fit, recent activity, talking, and measurement technique can affect readings. Record the time and circumstances rather than treating every number as equally comparable.
A home monitor is not automatically accurate for every person or arm size. Ask a healthcare professional about the device and technique, especially when readings are inconsistent with clinic measurements or symptoms.
Do not repeatedly check every few seconds in an attempt to obtain a preferred number. Follow the measurement schedule agreed with the care team.
Understand trends without self-diagnosing
A log can show whether readings remain elevated under comparable conditions. It can also help a clinician distinguish an isolated result from a pattern. Record both numbers, not just the one that looks unusual.
Medication, illness, stress, activity, and other circumstances can affect interpretation. Do not start, stop, or change prescribed medication based only on an online chart. A clinician can assess the broader picture and decide whether further evaluation is needed.
A reading in a “normal” category does not rule out an emergency when serious symptoms are present.
Keep pulse pressure and MAP in perspective
Pulse pressure is systolic minus diastolic pressure. For 120/80, it is 40 mm Hg. A common resting approximation for mean arterial pressure is diastolic + one-third of pulse pressure, giving about 93.3 mm Hg in that example.
These are different quantities with specific clinical uses and limitations. They do not replace the systolic/diastolic category table or provide a self-treatment target. An arithmetic result cannot determine whether circulation or organ perfusion is adequate in an individual.
Use the numbers to communicate clearly with a healthcare professional, and prioritize symptoms and appropriate care over a reassuring calculator label.
Frequently asked questions
Which number matters if only one is high?
Both matter. In the AHA category framework, the higher category indicated by either number governs the screening classification.
Can one reading diagnose hypertension?
A single reading generally does not establish the complete diagnosis. A clinician considers repeat measurements and the relevant medical context.
Should I wait for another reading if I have chest pain or stroke-like symptoms?
No. Seek emergency help immediately. Serious symptoms should not be dismissed or delayed because of a calculator result or a plan to recheck blood pressure.
Sources & calculation notes
Primary references are linked below. Dates, limits, and product terms can change; confirm the applicable details before acting.
Use this guide thoughtfully. Educational information, not a diagnosis or individualized medical advice. A screening result or formula cannot establish what is safe or appropriate for a particular person. Consult a qualified healthcare professional for clinical decisions.