Blood Pressure Calculator
Enter your systolic and diastolic readings to find your blood pressure category, based on American Heart Association guidelines.
American Heart Association blood pressure categories
| Category | Systolic (mmHg) | Diastolic (mmHg) | |
|---|---|---|---|
| Normal | Below 120 | and | Below 80 |
| Elevated | 120-129 | and | Below 80 |
| Hypertension Stage 1 | 130-139 | or | 80-89 |
| Hypertension Stage 2 | 140 or higher | or | 90 or higher |
| Hypertensive Crisis | Higher than 180 | and/or | Higher than 120 |
The higher of your two numbers determines your category — if your systolic reading falls in one category and your diastolic falls in a higher one, the higher category applies.
Systolic 128 falls in the "Elevated" range (120-129), but diastolic 82 falls in "Hypertension Stage 1" (80-89). Since the higher category governs, the overall reading is classified as Hypertension Stage 1.
Systolic 135 falls in "Hypertension Stage 1" (130-139), while diastolic 72 is comfortably within "Normal" (below 80). Even though the bottom number looks fine, the reading is still classified as Hypertension Stage 1 because the higher of the two numbers governs.
Compare this with the 128/82 example above, where the diastolic number was the one driving the classification. Together they show that neither number is "the important one" — both are checked independently, and whichever lands in the more severe category sets the overall result.
Why one reading isn't a diagnosis
Blood pressure fluctuates naturally throughout the day and can be temporarily elevated by caffeine, stress, physical activity, or even the anxiety of being at a doctor's office ("white coat syndrome"). A proper diagnosis of high blood pressure is based on the average of multiple readings taken on separate occasions, not a single number — this calculator is meant to help you understand where a given reading falls, not to diagnose a condition.
Factors that can temporarily affect a reading
| Factor | Typical effect |
|---|---|
| Caffeine (within ~30 minutes) | Temporary increase |
| "White coat syndrome" (at a doctor's office) | Temporary increase |
| Full bladder | Temporary increase |
| Talking during the measurement | Temporary increase |
| Unsupported arm or crossed legs | Temporary increase |
| Recent exercise | Temporary increase, then a dip below baseline |
None of these mean anything is wrong — they're simply why a single reading can vary from one measurement to the next. Sitting quietly for about five minutes beforehand, with feet flat and your arm supported at heart level, gives the most representative number.
Common mistakes when interpreting blood pressure readings
- Only looking at the systolic number. Either number being elevated is enough to move you into a higher category — check both.
- Treating a single reading as definitive. Multiple readings over time give a much more reliable picture.
- Ignoring a hypertensive crisis reading. A reading above 180/120 warrants retesting and, if confirmed, immediate medical attention — not a wait-and-see approach.
Frequently asked questions
What is a normal blood pressure reading?
Below 120/80 mmHg, per American Heart Association guidelines.
What's the difference between systolic and diastolic pressure?
Systolic (top number) is the pressure when your heart beats; diastolic (bottom number) is the pressure when it rests between beats.
What should I do if my reading falls in the hypertensive crisis range?
Wait five minutes and retest — if still above 180/120, seek immediate medical attention.
Is one high reading enough to be diagnosed with high blood pressure?
No — diagnosis is typically based on multiple readings across separate occasions, since readings fluctuate naturally.
Does caffeine or a full bladder affect a reading?
Yes — both can temporarily raise it by several mmHg. Waiting 30 minutes after caffeine or exercise and using the bathroom first gives a more representative number.
Which number determines the category if they fall in different ranges?
The higher category applies — whichever number, systolic or diastolic, lands in the more severe range sets the overall classification.
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Note: This tool is for educational purposes only and does not diagnose any medical condition. Consult a healthcare provider about your blood pressure readings. Source: American Heart Association. Last reviewed: September 2026.