A normal blood pressure reading is below 120/80 mmHg. That means the top number (systolic) is less than 120 and the bottom number (diastolic) is less than 80. Once either number climbs above those thresholds, your blood pressure falls into a higher category, even if the other number stays in range.
What the Two Numbers Mean
Blood pressure is measured in millimeters of mercury (mmHg) and written as two numbers separated by a slash. The top number, systolic pressure, measures the force of blood against your artery walls when your heart beats. The bottom number, diastolic pressure, measures that same force between beats, when the heart is briefly at rest. Both numbers matter, and either one being too high is enough to shift your reading out of the normal range.
Blood Pressure Categories
The American Heart Association and the American College of Cardiology define four categories for adults:
- Normal: Below 120 systolic and below 80 diastolic
- 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 that the categories use “and” for normal and elevated, but “or” for hypertension. If your systolic is 135 and your diastolic is 75, you still fall into Stage 1 hypertension because one number crossed the line. The higher category always wins.
The World Health Organization uses a slightly different threshold, diagnosing hypertension at 140/90 mmHg or higher. For most people globally, the WHO recommends keeping blood pressure below 140/90, with a stricter target of below 130/80 for those who already have heart disease, diabetes, or chronic kidney disease.
When Blood Pressure Is Too Low
There’s no official “low normal” cutoff the way there is for high blood pressure, but readings below 90/60 mmHg are generally considered low. Low blood pressure on its own isn’t a problem if you feel fine. It becomes a concern when it causes symptoms like dizziness, blurred vision, fatigue, or fainting. A sudden drop of even 20 mmHg in the systolic number, say from 110 to 90, can be enough to make you lightheaded.
When a Reading Becomes an Emergency
A reading of 180/120 mmHg or higher is classified as a hypertensive crisis. If that number shows up alongside chest pain, shortness of breath, severe headache, blurred vision, confusion, or symptoms of a stroke, it requires emergency medical attention. If the reading is that high but you feel fine, wait five minutes, then measure again. A single spike can happen from stress or a faulty reading, but consistently hitting those numbers needs prompt evaluation.
Why Your Reading Might Not Be Accurate
Blood pressure is surprisingly easy to measure incorrectly. The CDC recommends avoiding food, drink, caffeine, alcohol, nicotine, and exercise for at least 30 minutes before taking a reading. You should sit with your back supported and both feet flat on the floor for at least five minutes beforehand. Your arm should rest on a surface at chest height, legs uncrossed, and you shouldn’t talk during the measurement. Skipping any of these steps can artificially raise your numbers.
There’s also the issue of your body reacting differently depending on where you are. About 14% of people have what’s called white coat hypertension: their blood pressure reads high in a medical setting but is normal at home. Among people who show elevated readings at the doctor’s office, the rate is even higher, roughly 43% in one large international study. The reverse also happens. Nearly 10% of people have masked hypertension, meaning their numbers look fine in the clinic but run high in everyday life. This is why home monitoring over several days gives a more reliable picture than any single office visit.
How to Get a Reliable Baseline
One reading doesn’t define your blood pressure. It fluctuates throughout the day based on activity, stress, hydration, and even the time of day. To get a meaningful baseline, measure at the same time each day, ideally morning and evening, for at least a week. Take two or three readings each time, about a minute apart, and record them. Your average across those readings is far more useful than any individual number.
Home monitors with an upper arm cuff are generally more accurate than wrist models. If you’re comparing your home readings to what you get at a clinic, bring your home monitor to an appointment so the readings can be checked side by side. A consistent difference of more than 5 to 10 mmHg between devices suggests one of them needs recalibrating or replacing.
What Affects Your Numbers Over Time
Blood pressure tends to rise with age as arteries lose some of their elasticity. That said, the definition of “normal” doesn’t change: below 120/80 remains the goal regardless of age. The guidelines don’t give older adults a higher threshold for normal, though treatment targets for people with additional health conditions may be adjusted on a case-by-case basis.
Beyond age, the biggest drivers of blood pressure are sodium intake, physical activity, body weight, alcohol consumption, and stress. Genetics play a role too, but lifestyle factors account for a large share of the variation between individuals. If your readings are creeping into the elevated range (120 to 129 systolic), those are the levers most likely to bring them back down before medication becomes part of the conversation.