A normal blood pressure reading is less than 120/80 mmHg. That means the top number (systolic) stays below 120 and the bottom number (diastolic) stays below 80. Once either number climbs above those thresholds, the reading falls into elevated or high blood pressure territory.
What the Two Numbers Mean
Blood pressure is always written as two numbers separated by a slash. The top number, systolic pressure, measures the force inside your arteries when your heart beats and pushes blood out. The bottom number, diastolic pressure, measures the pressure in your arteries between beats, when your heart is briefly resting. Both numbers matter, and either one being too high is enough to change your category.
Blood Pressure Categories for Adults
The American Heart Association breaks adult blood pressure into four categories:
- Normal: Less than 120 systolic and less than 80 diastolic
- Elevated: 120 to 129 systolic and less than 80 diastolic
- Stage 1 hypertension: 130 to 139 systolic or 80 to 89 diastolic
- Stage 2 hypertension: 140 or higher systolic or 90 or higher diastolic
Notice that elevated blood pressure is defined entirely by the top number. If your systolic reading sits between 120 and 129 but your diastolic stays under 80, you’re in the elevated range. This is essentially a warning zone: not yet high blood pressure, but heading in that direction without lifestyle changes.
A reading of 180/120 or higher is considered a hypertensive crisis and requires emergency medical attention.
When Blood Pressure Is Too Low
A reading of 90/60 or lower is classified as low blood pressure. This isn’t necessarily a problem on its own. Low blood pressure only needs attention if it causes symptoms like dizziness, fainting, or lightheadedness. Some people naturally run on the lower side their entire lives without any issues.
Normal Ranges for Children and Teens
Children and adolescents have lower normal blood pressure than adults, and their expected ranges change with both age and height. A 10-year-old boy of average height, for example, has a typical reading around 102/61 mmHg. A reading at or above 121/81 for that same child would be at the 95th percentile and considered high.
Pediatric blood pressure isn’t evaluated using the same fixed cutoffs as adults. Instead, doctors compare a child’s reading against percentile charts that account for age, sex, and height. There’s no single “normal” number for kids the way there is for adults, which is why your child’s doctor interprets the reading rather than giving you a simple pass/fail.
How to Get an Accurate Reading
Blood pressure is surprisingly sensitive to how and when you measure it. Small details in your preparation can push a reading several points in either direction, potentially moving you from one category to another. The CDC recommends following these steps for the most reliable result:
- Avoid food, drinks, caffeine, alcohol, and exercise for at least 30 minutes before your reading.
- Empty your bladder before sitting down. A full bladder can raise your numbers.
- Sit with your back supported in a comfortable chair for at least 5 minutes before the measurement.
- Keep both feet flat on the floor with your legs uncrossed. Crossing your legs can increase your reading.
- Rest your arm on a table at chest height with the cuff against bare skin, not over clothing.
- Stay silent during the reading. Talking while the cuff inflates can affect the result.
Cuff size also matters. Cuffs are sized based on the circumference of your upper arm: small adult cuffs fit arms up to 26 cm, standard adult cuffs fit 27 to 34 cm, large adult cuffs fit 35 to 44 cm, and extra-large cuffs are for arms over 44 cm. Using a cuff that’s too small for your arm will give an artificially high reading.
Why Your Reading Can Vary by Setting
Some people consistently get high readings at the doctor’s office but have perfectly normal blood pressure at home. This is called white-coat hypertension, and it happens because the stress of a medical visit temporarily spikes blood pressure. It’s common enough that doctors are well aware of it.
The opposite pattern exists too. Masked hypertension means your blood pressure reads normal in the clinic but runs high during the rest of your day. This is trickier because it can go undetected for years if you’re only checked during office visits. Both conditions lead to unreliable in-office readings, which is why doctors sometimes recommend ambulatory monitoring, where you wear a portable cuff that takes readings throughout a full 24-hour period. This gives a much more complete picture than any single snapshot.
If your readings bounce around significantly between home and the clinic, tracking your numbers at home for a week or two and bringing that log to your appointment gives your doctor far better data to work with than a single office reading ever could.