What the Two Numbers Mean
Systolic — the top number — is the pressure in the arteries while the heart contracts. Diastolic is the pressure between beats, while the heart refills. Both matter, and the category is set by whichever is worse.
Blood Pressure Chart
| Category | Systolic | Diastolic | What it means | |
|---|---|---|---|---|
| Normal | Under 120 | and | Under 80 | Maintain healthy habits |
| Elevated | 120–129 | and | Under 80 | Lifestyle changes recommended |
| Hypertension stage 1 | 130–139 | or | 80–89 | Lifestyle changes; medication if risk is high |
| Hypertension stage 2 | 140 or above | or | 90 or above | Lifestyle changes and medication usually |
| Hypertensive crisis | Above 180 | or | Above 120 | Seek medical care immediately |
These are the 2017 ACC/AHA categories, which lowered the hypertension threshold from 140/90 to 130/80. The change reclassified roughly 31 million additional Americans as hypertensive, with the intent of earlier lifestyle intervention rather than earlier medication.
Pulse Pressure and Mean Arterial Pressure
Pulse pressure is systolic minus diastolic, normally 40–60 mmHg. A wide pulse pressure in older adults indicates arterial stiffening and independently predicts cardiovascular events. Mean arterial pressure — diastolic plus a third of the pulse pressure — approximates the average pressure driving organ perfusion, and needs to stay above roughly 60–70 mmHg.
Measuring It Correctly
Readings are easily distorted, usually upward:
- Sit quietly for five minutes first, back supported, feet flat, arm at heart level.
- No caffeine, exercise or smoking for 30 minutes beforehand.
- Empty your bladder — a full one adds 10–15 mmHg.
- Do not talk during the measurement, which adds another 10–15.
- Use a correctly sized cuff; one that is too small overestimates substantially.
- Take two or three readings a minute apart and average them.
White-coat hypertension — elevated readings only in clinical settings — affects 15–30% of people, which is why home monitoring is increasingly the basis for diagnosis.
What Lowers It
| Intervention | Typical systolic reduction |
|---|---|
| Weight loss | 1 mmHg per kg lost |
| DASH dietary pattern | 8–14 mmHg |
| Reducing sodium | 5–6 mmHg |
| Regular aerobic exercise | 5–8 mmHg |
| Limiting alcohol | 4 mmHg |
These are additive to a useful degree. Several combined frequently move stage 1 hypertension into the normal range without medication.
Frequently Asked Questions
Does one high reading mean I have hypertension?
No. Diagnosis requires elevated readings on at least two separate occasions, ideally supported by home or ambulatory monitoring.
Is low blood pressure a problem?
Only if it causes symptoms — dizziness, fainting, fatigue. A reading of 90/60 in someone who feels well is not a concern and is often a sign of fitness.
Why is it higher in one arm?
A small difference is normal. A consistent gap above 10–15 mmHg between arms warrants investigation, and the higher arm should be used for future readings.