About the Blood Pressure Calculator
A blood pressure reading is two numbers — systolic over diastolic, in millimetres of mercury — and the question everybody asks is what category it falls in.
The answer depends on three things most charts do not spell out.
The higher category wins. Systolic and diastolic are classified separately, and the reading takes whichever lands higher.
It depends which guideline you ask. The US and European guidelines start hypertension at different points, so the same reading can carry two different names.
One reading proves little. Blood pressure varies through the day, and guidelines judge it on averages.
This blood pressure calculator classifies your reading under both guidelines, averages up to three readings, and shows pulse pressure and mean arterial pressure alongside.
How to Use the Blood Pressure Calculator
Enter the systolic (top) and diastolic (bottom) numbers from your monitor.
If you have taken more than one reading, enter up to two more. Each needs both numbers. They are averaged before classifying, which is how guidelines expect blood pressure to be judged.
How Readings Are Classified
Each number is placed on its own scale, and the reading takes the higher category of the two.
2017 ACC/AHA (United States):
| Category | Systolic | Diastolic | |
|---|---|---|---|
| Normal | under 120 | and | under 80 |
| Elevated | 120–129 | and | under 80 |
| Stage 1 hypertension | 130–139 | or | 80–89 |
| Stage 2 hypertension | 140 or more | or | 90 or more |
| Hypertensive crisis | over 180 | and/or | over 120 |
2018 ESC/ESH (Europe):
| Category | Systolic | Diastolic | |
|---|---|---|---|
| Optimal | under 120 | and | under 80 |
| Normal | 120–129 | and/or | 80–84 |
| High normal | 130–139 | and/or | 85–89 |
| Grade 1 hypertension | 140–159 | and/or | 90–99 |
| Grade 2 hypertension | 160–179 | and/or | 100–109 |
| Grade 3 hypertension | 180 or more | and/or | 110 or more |
Step-by-Step Example
Two readings: 130/80 and 140/90.
Average systolic: (130 + 140) ÷ 2 = 135
Average diastolic: (80 + 90) ÷ 2 = 85
US guideline: 135 → stage 1, 85 → stage 1 → Stage 1 hypertension
European guideline: 135 → high normal, 85 → high normal → High normal
Pulse pressure: 135 − 85 = 50 mmHg
Mean arterial: 85 + 50 ÷ 3 = 102 mmHgThe same average is hypertension in the United States and not in Europe.
Why the Guidelines Disagree
In 2017 the American College of Cardiology and American Heart Association moved the start of hypertension down from 140/90 to 130/80. The European Society of Cardiology, reviewing much of the same evidence a year later, kept 140/90 and named the band below it "high normal".
Neither is wrong. The risk of a reading at 135/85 is the same in Boston as in Berlin. What differs is where each group chose to draw the line between advice about lifestyle and a diagnosis — and, with it, how many people are labelled.
In practice, both would recommend lifestyle changes at 135/85, and both decide on medicine by looking at overall cardiovascular risk rather than the reading alone.
Risk Rises Steadily, Not at a Line
Categories make the subject tidy, but the risk underneath them is a smooth slope.
Pooling a million adults across 61 studies, the Prospective Studies Collaboration found that from 115/75 upwards, every 20 mmHg of systolic (or 10 of diastolic) roughly doubled the risk of dying from heart disease or stroke, for people aged 40 to 69.
The encouraging corollary: lowering systolic pressure by 10 mmHg cuts major cardiovascular events by about a fifth. Less salt, less alcohol, regular activity and losing excess weight each typically lower it by several mmHg, and they add up.
Pulse Pressure and Mean Arterial Pressure
Pulse pressure is systolic minus diastolic, usually about 40. A gap of 60 or more often reflects stiffening arteries with age and is worth mentioning to a doctor.
Mean arterial pressure is the average pressure across a whole heartbeat: diastolic plus a third of the pulse pressure. Diastolic counts for more because the heart spends roughly two thirds of each beat relaxed.
Measuring It Properly at Home
Home readings are often more useful than clinic ones, because they avoid the rise many people show in front of a doctor, and because they can be averaged over days. They only help if they are taken consistently.
Sit for five minutes first, back supported, feet flat and legs uncrossed.
Rest your arm on a table so the cuff sits at the level of your heart, on bare skin rather than over a sleeve.
Stay quiet while it measures; talking alone can add several mmHg.
Take two readings a minute apart, morning and evening, for about a week, and discard the first day. The average of the rest is the figure that matters.
Use a validated upper-arm monitor with the right cuff size for your arm. Wrist monitors are more sensitive to position and read less reliably.
Understanding Your Result
Your reading shows the average and its category under the US guideline.
Under both guidelines gives the US and European categories side by side.
Pulse and mean pressure adds the two derived figures.
Readings used lists what was averaged, or notes a single reading.
Worth knowing covers what the category means, where the guidelines disagree, or a crisis-level reading that needs acting on.
When Should You Use This Calculator?
After measuring at home, to see what your average means.
When a US chart and a UK or European leaflet seem to disagree.
To check whether one number is driving the category.
Not in place of a doctor when readings are persistently raised, or with symptoms.
Common Mistakes
Reading the chart along one number. The higher category wins.
Judging on a single reading. Averages across days are what count.
Measuring straight after coffee, exercise or a cigarette. Wait half an hour.
Using the wrong cuff size. Too small reads high; too large reads low.
Talking, crossing legs or letting the arm hang. Each adds several mmHg.
A reading above 180/120 should be rechecked after five minutes; if it stays that high, get medical help promptly, and call emergency services at once with chest pain, breathlessness, weakness or trouble speaking. Nothing here is medical advice.