A blood pressure reading has two numbers, written as one over the other, like 120/80. The top number (systolic) measures the force of blood pushing against your artery walls when your heart beats. The bottom number (diastolic) measures that pressure between beats, when your heart is resting and refilling. Both numbers are measured in millimeters of mercury, abbreviated as mm Hg.
What the Categories Mean
The American Heart Association and American College of Cardiology define four blood pressure categories for adults:
- Normal: Below 120/80 mm Hg
- Elevated: 120 to 129 systolic and below 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 the word “or” in the hypertension stages. If either number crosses the threshold, the higher category applies. So a reading of 138/72 counts as Stage 1 hypertension even though the bottom number looks fine. Likewise, 118/92 qualifies as Stage 2 because of the diastolic reading alone.
Elevated blood pressure is a warning zone. It means the top number is creeping up, but the bottom number is still healthy. Without changes, elevated blood pressure tends to progress into full hypertension over time.
When Blood Pressure Becomes an Emergency
A reading of 180/120 or higher is considered a hypertensive crisis. If you see numbers that high and also have symptoms like chest pain, severe headache, blurred vision, confusion, shortness of breath, or numbness on one side of your body, that’s a medical emergency. These symptoms can signal a stroke or organ damage in progress.
If your reading hits 180/120 without symptoms, wait five minutes and measure again. A single spike from stress or exertion isn’t necessarily dangerous, but consistently reaching those numbers warrants urgent medical attention.
The Gap Between the Two Numbers
The difference between your top and bottom numbers is called pulse pressure. If your reading is 120/80, your pulse pressure is 40, which is considered healthy. A pulse pressure consistently above 60 is a risk factor for heart disease, particularly in older adults, because it suggests the large arteries are becoming stiff and less elastic. The wider that gap, the more wear and tear your blood vessels have likely accumulated.
How Blood Pressure Differs in Children
Children naturally have lower blood pressure than adults, and what counts as “normal” depends on age, sex, and height. A typical one-year-old might have a reading around 80/34, while a 17-year-old boy at average height typically runs about 114/65. A 17-year-old girl at average height averages around 108/64. Pediatric blood pressure is evaluated using percentile charts rather than the fixed cutoffs used for adults, so a number that’s perfectly normal for a teenager could be concerning for a toddler.
Home Readings vs. Office Readings
Blood pressure measured at a doctor’s office tends to run slightly higher than what you’d see at home, partly because of the stress of being in a medical setting. The thresholds reflect this: a home reading of 135/85 roughly corresponds to an office reading of 140/90. If you’re monitoring at home, keep that difference in mind when comparing your numbers to the standard categories, which are based on office measurements.
For the most accurate home reading, sit in a comfortable chair with your back supported for at least five minutes before taking a measurement. Rest the arm wearing the cuff on a table at chest height. The cuff should sit against bare skin, snug but not tight, and you should avoid talking during the reading. Taking two or three readings a minute apart and averaging them gives you a more reliable number than any single measurement.
When Treatment Starts
Lifestyle changes are the first-line approach at every stage of high blood pressure. That includes reducing sodium, increasing physical activity, managing weight, and limiting alcohol. At Stage 2 (140/90 or above), medication is recommended for most adults alongside those changes.
Stage 1 hypertension (130 to 139 over 80 to 89) is treated more selectively. Medication at this stage is typically recommended if you already have heart disease, diabetes, kidney disease, or if your estimated 10-year risk of a cardiovascular event is 10% or higher. Otherwise, you’ll generally get three to six months to bring the numbers down through lifestyle changes before medication enters the conversation.
For adults over 80, treatment thresholds are more conservative. Some guidelines recommend starting medication only when systolic pressure reaches 160, because the risks and benefits of aggressive blood pressure lowering shift with age.
Why One Reading Isn’t Enough
Blood pressure fluctuates throughout the day. It rises when you exercise, feel stressed, or drink caffeine, and it drops while you sleep. A single high reading doesn’t mean you have hypertension. Diagnosis is based on a pattern of elevated readings across multiple visits or through sustained home monitoring. If your numbers come back high at a checkup, you’ll typically be asked to confirm with additional measurements before any treatment decisions are made.