A normal blood pressure reading is less than 120/80 mm Hg. That means a systolic (top) number under 120 and a diastolic (bottom) number under 80. Once either number climbs above those thresholds, your blood pressure falls into the elevated or high range.
What the Two Numbers Mean
A blood pressure reading always has two numbers. The top number, systolic pressure, measures the force your blood pushes against artery walls each time your heart beats. The bottom number, diastolic pressure, measures that same force between beats, when your heart is resting. Both numbers matter, and either one being too high is enough to move you out of the normal range.
Readings are measured in millimeters of mercury, abbreviated mm Hg. So when you see “120/80 mm Hg,” it means the peak pressure during a heartbeat is 120 and the resting pressure between beats is 80.
Blood Pressure Categories
The American Heart Association defines five blood pressure categories for adults:
- Normal: Less than 120/80 mm Hg. No treatment needed, just healthy habits to maintain it.
- Elevated: Systolic between 120 and 129, with diastolic still under 80. This is the early warning zone. Blood pressure at this level tends to get worse over time without lifestyle changes.
- High blood pressure, Stage 1: Systolic 130 to 139, or diastolic 80 to 89. At this point, your doctor will likely recommend diet and exercise changes, and possibly medication depending on your overall heart disease risk.
- High blood pressure, Stage 2: Systolic 140 or higher, or diastolic 90 or higher. This stage typically involves both lifestyle changes and medication.
- Hypertensive crisis: Systolic over 180 and/or diastolic over 120. This is a medical emergency, especially with symptoms like chest pain, shortness of breath, severe headache, blurred vision, confusion, or seizures.
Notice that the categories use “or” between systolic and diastolic. If your top number is 138 but your bottom number is 75, you still fall into Stage 1. The higher category always wins.
When Blood Pressure Is Too Low
A reading below 90/60 mm Hg is generally considered low blood pressure. But unlike high blood pressure, low readings aren’t automatically a problem. Many people walk around with naturally low blood pressure and feel perfectly fine. It only becomes a concern when it causes symptoms like dizziness, fainting, fatigue, or blurred vision.
Sudden drops deserve more attention than consistently low readings. A fall of just 20 mm Hg, from 120 to 100 systolic for example, can be enough to make you lightheaded or faint, even though 100 is technically a normal number. This commonly happens when you stand up quickly, especially in older adults.
Normal Ranges for Children and Teens
Children naturally have lower blood pressure than adults, and what counts as “normal” depends on age, sex, and height. A one-year-old boy at average height typically reads around 85/37 mm Hg. By age eight, that climbs to roughly 99/59. A 17-year-old boy averages about 118/67, which is close to the adult normal range.
Girls follow a similar pattern but tend to run slightly lower, especially in the teen years. A 17-year-old girl at average height typically reads around 111/66. Pediatricians use percentile charts that account for a child’s specific height and age rather than a single cutoff number, so a reading that’s normal for a tall 12-year-old might be elevated for a short one.
How to Get an Accurate Reading
Blood pressure is surprisingly sensitive to how and when you measure it. A poorly taken reading can be off by 10 mm Hg or more, which is enough to bump you from normal into the elevated category (or vice versa). The CDC recommends a specific routine to get a reliable number.
Avoid eating, drinking, or exercising for 30 minutes beforehand. Empty your bladder. Then sit in a chair with your back supported and both feet flat on the floor, legs uncrossed, for at least five minutes before taking the reading. Your arm should rest on a table at chest height with the cuff snug around bare skin. Don’t talk during the measurement.
Cuff size matters more than most people realize. A cuff that’s one size too small can overestimate your reading by 5 to 10 mm Hg, while one that’s too large can underestimate it by a similar margin. If you’re using a home monitor, check that the cuff fits your arm circumference. Most standard cuffs accommodate arms up to about 13 inches around, which isn’t large enough for many adults.
White Coat Hypertension
Somewhere between 15% and 30% of people who show elevated blood pressure at the doctor’s office have normal readings at home. This is called white coat hypertension, and it happens because the stress of a medical visit temporarily raises your numbers. If your readings are consistently high at the office but you suspect anxiety is playing a role, home monitoring over several days gives a more accurate picture. Take two or three readings each time, a minute apart, and track the average.
What Affects Your Numbers Day to Day
Blood pressure isn’t a fixed number. It fluctuates throughout the day based on activity, stress, hydration, and even body position. It’s typically lowest during sleep and rises in the morning. Caffeine, a full bladder, cold temperatures, and emotional stress can all push readings higher temporarily.
This is why a single reading doesn’t tell you much. A diagnosis of high blood pressure is based on elevated readings taken on two or more separate occasions, measured correctly each time. If you get a high number at a pharmacy kiosk or a one-off doctor visit, it’s worth confirming with repeated measurements at home before drawing conclusions.
Blood pressure also tends to rise with age as arteries become stiffer and less elastic. Someone who had a reading of 110/70 at age 25 may see that creep toward 130/80 by their 50s or 60s, even without major changes in weight or diet. That progression isn’t inevitable, but it is common, which is why regular monitoring becomes more important over time.