A blood pressure reading gives you two numbers, like 120/80. The top number (systolic) measures the pressure in your arteries when your heart beats and pushes blood out. The bottom number (diastolic) measures the pressure between beats, when your heart is resting. Both numbers are measured in millimeters of mercury (mm Hg), and together they tell you how hard your blood is pushing against your artery walls.
What the Categories Mean
The American Heart Association and American College of Cardiology define four blood pressure categories for adults. If your top and bottom numbers fall into different categories, the higher category is the one that applies to you.
- Normal: Below 120/80 mm Hg. Both numbers need to be under these thresholds.
- Elevated: Systolic 120 to 129, with diastolic still under 80. This is a warning zone. Your blood pressure isn’t high enough to be called hypertension yet, but it’s trending in that direction.
- Stage 1 Hypertension: Systolic 130 to 139, or diastolic 80 to 89. At this level, lifestyle changes become important, and your doctor may discuss medication depending on your overall heart disease risk.
- Stage 2 Hypertension: Systolic 140 or higher, or diastolic 90 or higher. This typically calls for both lifestyle changes and medication.
Notice that only one number needs to cross the threshold. A reading of 145/75 counts as Stage 2 hypertension even though the bottom number looks fine. This is common in older adults, whose arteries stiffen with age and drive the top number up while the bottom number stays the same or even drops.
When Blood Pressure Is Too Low
A reading below 90/60 mm Hg is generally considered low blood pressure, or hypotension. But low numbers only matter if they’re causing symptoms. Some people walk around at 90/60 their whole lives and feel perfectly fine.
What does matter is sudden drops. A systolic decrease of just 20 points, say from 110 to 90, can make you feel dizzy or faint. If you regularly feel lightheaded when standing up, get blurry vision, or feel unusually fatigued, your blood pressure may be dropping too far at certain times of day.
The Gap Between the Numbers
The difference between your top and bottom numbers is called pulse pressure. If your reading is 130/70, your pulse pressure is 60. A healthy pulse pressure is generally around 40 mm Hg. Once it climbs above 60, it becomes a meaningful risk factor for heart attacks and strokes, particularly in older adults.
A wide pulse pressure usually signals that your largest arteries have stiffened. The stiffer and more damaged those vessels are, the greater the gap tends to be. This is why two people with the same systolic number can have very different cardiovascular risk profiles. Someone reading 150/90 (pulse pressure of 60) and someone reading 150/110 (pulse pressure of 40) face different types of concern, even though both have high blood pressure.
Why High Blood Pressure Damages Your Body
High blood pressure rarely causes symptoms you can feel, which is why it’s often called a silent condition. But sustained pressure above normal slowly damages blood vessels throughout your body, and the organs that depend on those vessels pay the price.
Your heart has to pump harder against that extra resistance. Over time, the heart muscle thickens and stiffens, and eventually it can weaken and lose its ability to pump efficiently. The arteries feeding the heart itself can narrow and harden, restricting blood flow and raising the risk of chest pain or a heart attack.
Your brain is equally vulnerable. Damaged blood vessels can narrow, leak, or develop clots, all of which can block blood supply to parts of the brain. This can cause a stroke or a transient ischemic attack (a brief, stroke-like episode where blood flow is temporarily cut off). Long-term high blood pressure is also linked to cognitive decline, with subtle changes in memory and thinking that accumulate over years.
Your kidneys filter waste from your blood through an intricate network of tiny blood vessels. When high blood pressure damages those vessels, the kidneys gradually lose their filtering ability. Having diabetes alongside high blood pressure accelerates this damage significantly.
Factors That Temporarily Shift Your Numbers
Blood pressure isn’t a fixed number. It fluctuates throughout the day based on what you’re doing, eating, and feeling. Salty foods, alcohol, caffeine, poor sleep, and physical activity can all push your reading higher in the short term. Emotional stress is another common trigger. Some people see their numbers spike specifically in a medical setting, a phenomenon sometimes called white coat hypertension, simply because the environment makes them anxious.
This is why a single high reading doesn’t necessarily mean you have hypertension. Doctors typically look at patterns across multiple readings before making a diagnosis. If you tend to feel stressed during blood pressure checks, mention it. Small adjustments, like sitting quietly in a room for a few minutes before the measurement, can make a difference.
How to Get an Accurate Reading
The way you take your blood pressure matters more than most people realize. A poorly positioned arm or a full bladder can throw off your numbers enough to change which category you fall into. The CDC recommends following these steps for a reliable reading:
- Rest first. Sit in a comfortable chair with your back supported for at least 5 minutes before measuring.
- Skip food and drinks. Don’t eat or drink anything for 30 minutes beforehand.
- Empty your bladder. A full bladder can raise your reading.
- Position your body correctly. Keep both feet flat on the floor, legs uncrossed, and rest the cuffed arm on a table at chest height.
- Use bare skin. Place the cuff directly on your arm, not over clothing. It should be snug but not tight.
- Stay quiet. Don’t talk during the measurement.
If you’re monitoring at home, take two or three readings a minute apart and record all of them. Morning readings before medication or food tend to give the most consistent baseline.
When a Reading Is an Emergency
A blood pressure reading of 180/120 mm Hg or higher is considered a hypertensive crisis. If that reading comes with symptoms like severe headache, chest pain, shortness of breath, blurred vision, or seizures, it requires emergency medical care. These symptoms can signal active damage to your heart, brain, or other organs. If you get a reading that high but feel fine, wait five minutes and measure again. If it’s still at or above 180/120, contact your healthcare provider immediately.