What does my blood pressure reading mean?
It tells you which category the reading falls in. If the top and bottom numbers point to different categories, the higher one counts. Blood pressure is written as systolic over diastolic, in mmHg. The systolic (top number) is the peak pressure as the heart beats. The diastolic (bottom number) is the pressure while the heart refills.
The calculator uses one of two published systems. The US AHA/ACC 2017 guideline is the default in English; the European ESH 2023 guidelines are the other option. Both classify office readings taken at rest, in adults. The 2025 AHA/ACC update kept the same categories and thresholds as 2017.
Blood pressure chart: AHA/ACC 2017 categories
These are the US categories, as the calculator applies them. If the systolic and diastolic fall in different rows, the higher row counts.
| Category | Systolic (mmHg) | Diastolic (mmHg) | |
|---|---|---|---|
| Normal | below 120 | and | below 80 |
| Elevated | 120–129 | and | below 80 |
| Stage 1 hypertension | 130–139 | or | 80–89 |
| Stage 2 hypertension | 140 or higher | or | 90 or higher |
| Severe: hypertensive crisis range | above 180 | and/or | above 120 |
European blood pressure chart: ESH 2023 categories
The ESH system keeps the hypertension threshold at 140/90 and splits the range below it into three bands.
| Category | Systolic (mmHg) | Diastolic (mmHg) | |
|---|---|---|---|
| Optimal | below 120 | and | below 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 higher | and/or | 110 or higher |
| Isolated systolic hypertension | 140–159 | and | below 90 |
ESH grades isolated systolic hypertension by the systolic value. So from 160 systolic the calculator shows Grade 2 or Grade 3, even when the diastolic is below 90.
What is a normal blood pressure?
For adults, below 120/80 mmHg is normal under AHA/ACC 2017 and optimal under ESH 2023. The two systems part ways just above that. A reading of 126/78 is Elevated in the US system and Normal in the European one. At 134/82 the US system already says Stage 1 hypertension, while ESH says High normal.
Neither label is a diagnosis on its own. Both guidelines base it on several readings, taken the right way.
When is blood pressure high?
Under ESH 2023, hypertension starts at 140 systolic or 90 diastolic, measured in the office. AHA/ACC 2017 sets a lower threshold, 130/80. From 180 systolic or 110 diastolic, ESH calls it grade 3, the highest band.
How to use the blood pressure calculator
- Enter the Systolic (top number) in mmHg.
- Enter the Diastolic (bottom number) in mmHg. It must be lower than the systolic, or the calculator stops with an error.
- Under Categories, keep AHA/ACC 2017 (US) or switch to ESH 2023 (Europe).
- Read the Category, then the Mean arterial pressure and Pulse pressure underneath.
Mean arterial pressure is (systolic + 2 × diastolic) ÷ 3, rounded to a whole number. Pulse pressure is systolic minus diastolic. The mean arterial pressure calculator explains both in more detail.
Worked examples
Example 1 – a normal reading. 118/76 mmHg. Neither number reaches a higher band → Normal (AHA/ACC 2017), Optimal (ESH 2023). MAP: (118 + 2 × 76) ÷ 3 = 270 ÷ 3 = 90 mmHg. Pulse pressure: 118 − 76 = 42 mmHg.
Example 2 – where the two systems disagree. 134/82 mmHg. AHA/ACC 2017: the systolic is in 130–139 → Stage 1 hypertension. ESH 2023: the systolic is in 130–139 and the diastolic below 85 → High normal. MAP: (134 + 2 × 82) ÷ 3 = 298 ÷ 3 = 99.3 → 99 mmHg. Pulse pressure: 52 mmHg.
Example 3 – a high top number only. 152/84 mmHg. AHA/ACC 2017: systolic 140 or higher → Stage 2 hypertension. ESH 2023: systolic 140–159 with diastolic below 90 → Isolated systolic hypertension. MAP: (152 + 2 × 84) ÷ 3 = 320 ÷ 3 = 106.7 → 107 mmHg. Pulse pressure: 68 mmHg.
In all three cases the calculator adds the same note: one reading is not a diagnosis.
How to measure blood pressure correctly
Small slips in technique can shift a reading by several mmHg. Both guidelines recommend the same basic routine.
- Before: no caffeine, smoking or exercise for 30 minutes, and an empty bladder.
- Position: seated, back supported, feet flat on the floor, legs uncrossed.
- Rest: 5 minutes seated and quiet before the first reading, with no talking during it.
- Arm: bare upper arm, resting on a table so the cuff is at heart level.
- Cuff: the right size for your arm. A cuff that is too small reads high, one that is too large reads low.
- Repeat: at least 2 readings, 1–2 minutes apart, averaged. ESH suggests 3 readings and averaging the last two.
At a first check, both arms are usually measured, and the arm with the higher reading is used from then on.
Home readings versus office readings
Home averages use slightly lower thresholds than readings taken in the clinic. Readings at home are often lower than in the office, partly because there is no “white-coat” effect.
| Guideline | Office reading | Equivalent home average |
|---|---|---|
| ESH 2023: hypertension | 140/90 mmHg | 135/85 mmHg |
| AHA/ACC 2017: stage 1 | 130/80 mmHg | 130/80 mmHg |
| AHA/ACC 2017: stage 2 | 140/90 mmHg | 135/85 mmHg |
The calculator applies the office thresholds. For home monitoring, a usual pattern is two readings in the morning and two in the evening, over several days, ideally a week. The average of those readings is what counts, not any single one.
Why one reading is not a diagnosis
Blood pressure changes from minute to minute. Stress, pain, a full bladder, talking, coffee or a cuff of the wrong size can all push it up. Both guidelines confirm hypertension only on repeated readings, over more than one occasion, ideally with home or 24-hour ambulatory measurements.
If one reading is high, we suggest sitting quietly and measuring again later. A pattern over days tells your doctor far more than one number.
If a reading is very high and you have chest pain, shortness of breath, weakness, or trouble seeing or speaking, we recommend calling your local emergency number.
Low blood pressure
Neither guideline chart has a low category. Readings below 90/60 mmHg are often called low, and the calculator shows a note when the systolic is under 90 or the diastolic under 60.
Low pressure is often harmless. Many fit, healthy people run at those levels without symptoms. It deserves a check when it causes dizziness, fainting or blurred vision, when it is new, or when it comes with illness, bleeding or dehydration. In sick patients, a low reading together with a fast pulse is a warning sign; the shock index calculator puts those two numbers together.
What about blood pressure by age charts?
The adult categories do not change with age. Many websites show “normal blood pressure by age” charts with higher values for older people. Those charts describe what is common at each age, not what the guidelines call normal. Systolic pressure does tend to rise with age, which is why isolated systolic hypertension is common in older adults.
A doctor may set a different treatment goal for an individual, for example in frailty. That is a clinical decision, not a different chart. Children and teenagers are the real exception: their blood pressure is judged on percentile tables by age, sex and height. Our guide to normal vital signs by age has the paediatric ranges.
Frequently asked questions
What is a normal blood pressure?
For adults, below 120/80 mmHg. The AHA/ACC 2017 guideline calls this Normal, and the ESH 2023 guidelines call it Optimal. ESH still counts readings up to 129/84 as Normal, while the US guideline labels 120–129 systolic as Elevated. Both use office readings taken properly, not a single number on a bad day.
Is 130/80 high blood pressure?
It depends on the guideline. AHA/ACC 2017 places 130/80 in Stage 1 hypertension, because its stage 1 starts at 130 systolic or 80 diastolic. ESH 2023 calls the same reading High normal, since its hypertension threshold is 140/90. Either way, a single reading needs repeating before anyone draws conclusions.
Is 140/90 high blood pressure?
Yes, under both systems, if it is confirmed on repeated readings. AHA/ACC 2017 places 140/90 in Stage 2 hypertension, and ESH 2023 places it in Grade 1 hypertension. The label differs because the two guidelines draw their lines in different places, not because they disagree about the reading.
Which number matters more, the top or the bottom?
Both count, and the higher category wins. A reading of 125/88 is Stage 1 under AHA/ACC 2017 and High normal under ESH 2023, in both cases because of the diastolic alone. In younger adults the diastolic is more often the raised one. With age, arteries stiffen, the systolic tends to rise and the diastolic often falls, so isolated systolic hypertension becomes common.
Why do US and European categories differ?
They weigh the same evidence differently. AHA/ACC 2017 lowered the hypertension threshold to 130/80 to flag risk earlier. ESH 2023 kept 140/90 and added a High normal band below it. It makes sense to use the system your doctor or your country follows. The calculator shows either, and the reading itself does not change.
What blood pressure is too low?
There is no single cut-off. Readings below 90/60 mmHg are often called low, and the calculator flags them. Many healthy people, especially young and slim adults, live at those levels without symptoms. Low pressure matters when it causes dizziness, fainting or confusion, or when it is new for that person.
Does normal blood pressure change with age?
For adults the categories stay the same at every age. Blood pressure tends to rise with age, but that makes higher readings more common, not more normal. Children are different: their pressure is read on percentile tables by age, sex and height, so this calculator is meant for adults.
Can I use this calculator in pregnancy?
Not to interpret a reading. Pregnancy has its own thresholds and checks, and a raised reading can be an early sign of pre-eclampsia, which is best assessed promptly by a midwife or doctor. The MAP and pulse pressure arithmetic still works, but the categories here were written for non-pregnant adults.
Sources
- Whelton PK et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults. Hypertension 2018;71(6):e13–e115 (PMID 29133356)
- 2025 AHA/ACC Guideline for the Prevention, Detection, Evaluation and Management of High Blood Pressure in Adults. Hypertension 2025;82(10):e212–e316
- Mancia G et al. 2023 ESH Guidelines for the management of arterial hypertension. J Hypertens 2023;41(12):1874–2071 (PMID 37345492)