What is Blood Pressure?

The two numbers

Systolic is the pressure during a heartbeat; diastolic is the pressure between beats. For example, 122/78 means systolic 122 and diastolic 78 mmHg.

The standard categories

These are the AHA's U.S. adult categories, not individual treatment targets or pediatric guidance:

• Normal: systolic below 120 AND diastolic below 80.
• Elevated: systolic 120–129 AND diastolic below 80.
• Stage 1: systolic 130–139 OR diastolic 80–89.
• Stage 2: systolic at least 140 OR diastolic at least 90.

Use the higher category when the numbers differ: 118/91 is in the Stage 2 range. A clinician confirms the diagnosis.

When a reading needs urgent attention

Above 180 systolic and/or 120 diastolic, with chest pain, breathlessness, weakness, vision changes or difficulty speaking: call 911 in the U.S. Without symptoms, wait at least one minute and recheck; if still that high, contact your healthcare professional immediately. See the AHA's severe-hypertension and emergency guidance. Pregnancy requires specific clinical guidance.

How to measure it at home

Follow the AHA home-monitoring instructions and your clinician's plan:

1. Use a validated upper-arm monitor with the correct cuff size.
2. Avoid smoking, caffeine and exercise for 30 minutes beforehand; empty your bladder.
3. Rest quietly for at least five minutes. Do not talk or use your phone.
4. Place the cuff on bare skin and support the arm at heart level.
5. Take two readings, one minute apart, and record both.
6. Use consistent measurement times; agree frequency with your clinician.

Home monitoring complements appointments. Do not stop or change blood-pressure medication based on a log without speaking to your healthcare professional.

Make the record useful

Keep a separate row for each reading, with its date, time and any relevant notes. Preserve unexpected readings rather than deleting them to make a chart smoother. Bring the record and your questions to appointments.

Our home tracking and annual checkup guide discusses the role of home records, and the wearable guide links to the same AHA monitoring reference. See also resting heart rate.