Blood Pressure Calculator

This calculator is for educational and tracking purposes only. It is NOT a substitute for medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about any blood-pressure concern.

Blood pressure is one of the most-measured vital signs in modern medicine, and for good reason: it captures how hard the heart is working, how stiff the large arteries are, and how well blood is reaching every organ. A single home reading tells you a snapshot. A week of readings, plotted alongside pulse pressure and mean arterial pressure, gives a much better picture of cardiovascular load, and that is the picture this calculator is built to draw. It implements the five categories defined by the 2017 American College of Cardiology / American Heart Association (ACC/AHA) guideline (Whelton et al., Journal of the American College of Cardiology, 71(19):e127-e248), together with the unit conversions used in clinical measurement and the day-by-day averaging that home-monitoring programmes recommend.

How to Use This Calculator

1. Open the Classify reading tab. Enter a systolic value (the higher number, the pressure when the heart contracts) and a diastolic value (the lower number, the pressure when the heart relaxes), both in millimetres of mercury (mmHg).
2. Read the result panel. The headline colour-coded category appears at the top, followed by pulse pressure, mean arterial pressure, and an optional informational age / sex risk bucket.
3. Use the 7-day tracker tab to log a week's worth of home readings. The summary shows the daily average, the average MAP, and the systolic and diastolic range across the week.
4. Use the Convert units tab if your clinician reports your reading in kilopascals (kPa) or centimetres of water (cmH₂O), for example after a hospital measurement.
5. Optional: enter an age and sex in the classify tab to see a non-clinical risk bucket alongside the AHA category. This is informational only and is not a cardiovascular risk score.

What this calculator does

The calculator accepts a single systolic/diastolic reading and returns five pieces of information. First, the AHA / ACC 2017 category, Normal, Elevated, Stage 1 Hypertension, Stage 2 Hypertension, or Hypertensive Crisis. Second, the pulse pressure (PP), defined as the difference between systolic and diastolic, which is a proxy for arterial stiffness. Third, the mean arterial pressure (MAP), the time-weighted average pressure across one cardiac cycle, computed as DBP + 0.4 × (SBP − DBP). Fourth, a non-clinical risk bucket that combines the category with optional age and sex input. Fifth, a plain-language advisory for that category. The 7-day tracker adds three more: a 7-day systolic average, a 7-day diastolic average, and a 7-day MAP average. The unit converter adds the three live mmHg ↔ kPa ↔ cmH₂O pairs that clinical monitors and lab equipment routinely use.

AHA 2017 categories

The 2017 ACC/AHA guideline lowered the threshold for hypertension from the older 140/90 mmHg to 130/80 mmHg, doubling the number of US adults classified as hypertensive at a stroke. The five categories used here are:

• Normal. Systolic below 120 mmHg and diastolic below 80 mmHg. About 40% of US adults fall in this band. Maintain current lifestyle; recheck annually.
• high. Systolic 120 to 129 mmHg and diastolic below 80 mmHg. The diastolic restriction matters: a 125/85 reading is not high, it is Stage 1. About 12% of US adults are in this band; lifestyle changes (diet, exercise, weight, sodium) are first-line.
• Stage 1 hypertension. Systolic 130 to 139 mmHg or diastolic 80 to 89 mmHg. About 26% of US adults. Lifestyle changes are first-line; medication is added if the 10-year cardiovascular risk exceeds 10% or if other risk factors are present.
• Stage 2 hypertension. Systolic at or above 140 mmHg or diastolic at or above 90 mmHg. About 14% of US adults. Two medications from different classes are typically recommended alongside lifestyle change.
• Hypertensive crisis. Systolic above 180 mmHg and/or diastolic above 120 mmHg. This is a medical emergency, particularly when paired with chest pain, vision changes, shortness of breath, severe headache, or neurological symptoms. Call emergency services.

The five categories are checked in order from most-severe to least-severe. Hypertensive crisis is checked first because its threshold (SBP > 180 / DBP > 120) is a strict subset of Stage 2; checking Stage 2 first would mistakenly label a 185/95 reading as merely Stage 2 instead of crisis.

Mean arterial pressure

Mean arterial pressure (MAP) is the average arterial pressure across one cardiac cycle. Because the heart spends more time in diastole than in systole, MAP is closer to diastolic than to systolic, and the textbook formula uses a 0.4/0.6 weighting:

MAP = DBP + 0.4 × (SBP − DBP) = (2 × DBP + SBP) / 3

The two forms are algebraically identical. Normal MAP is roughly 70 to 100 mmHg. MAP is the figure that intensive-care units and anaesthetic protocols watch most closely, because coronary and cerebral perfusion pressure scale with MAP, not with systolic alone. Persistent MAP below 65 mmHg is associated with organ hypoperfusion; persistent MAP above 110 mmHg is associated with increased cardiovascular strain. Pulse pressure (PP = SBP − DBP) is a related measure: a wide PP (above 60 mmHg) in an older adult suggests arterial stiffening, while a narrow PP (below 25 mmHg) can suggest aortic stenosis or tamponade.

When to see a doctor

• Normal range, no symptoms. Annual check-ups are sufficient. Most guidelines suggest home monitoring only if you have other risk factors.
• high range. Bring it up at the next routine visit. Consider a six-month follow-up. Lifestyle changes are usually enough.
• Stage 1 range, low overall cardiovascular risk. Discuss at your next routine visit. Your clinician may recommend a confirmatory second reading over 1 to 4 weeks before committing to treatment.
• Stage 1 range, higher cardiovascular risk (existing cardiovascular disease, diabetes, chronic kidney disease, 10-year ASCVD risk ≥ 10%). Schedule a visit within weeks. Medication is often added to lifestyle changes.
• Stage 2 range. Schedule a clinical evaluation within days to weeks. Two medications from different classes are typically recommended.
• Hypertensive crisis without warning symptoms (no chest pain, no neurological deficit). Call your clinician or an urgent care line for guidance, urgent (but not emergency-room) re-evaluation is usually appropriate.
• Hypertensive crisis with warning symptoms. Call emergency services (911 in the US, 999 in the UK, 112 in the EU) immediately. Do not drive yourself.

Worked examples

The five cases below are the hand-verified test cases from the implementation. Each one matches the displayed category, pulse pressure, and mean arterial pressure to within rounding.

Example 1, Normal. 120/80 → Normal. PP = 120 − 80 = 40 mmHg. MAP = 80 + 0.4 × 40 = 96 mmHg. Recheck in a year.

Example 2, Stage 2 hypertension. 145/92 → Stage 2 hypertension. PP = 145 − 92 = 53 mmHg. MAP = 92 + 0.4 × 53 = 92 + 21.2 = 113.2 mmHg. Schedule a clinical evaluation.

Example 3, Normal-low. 90/60 → Normal (under the AHA thresholds: SBP < 120 AND DBP < 80). The calculator flags a low-systolic advisory because values this low can cause orthostatic symptoms. PP = 90 − 60 = 30 mmHg. MAP = 60 + 0.4 × 30 = 72 mmHg.

Example 4, Stage 1 hypertension. 130/85 → Stage 1 hypertension (SBP 130 to 139, DBP 80 to 89; the OR rule fires because both ranges overlap). PP = 130 − 85 = 45 mmHg. MAP = 85 + 0.4 × 45 = 85 + 18 = 103 mmHg.

Example 5, Hypertensive crisis. 181/121 → Hypertensive crisis (SBP > 180 AND DBP > 120). The calculator displays the emergency-services advisory. PP = 181 − 121 = 60 mmHg. MAP = 121 + 0.4 × 60 = 121 + 24 = 145 mmHg.

Where It Shows Up

Primary care. Every routine adult visit includes a blood-pressure reading. The 2017 ACC/AHA thresholds are the ones clinicians use when they decide whether to start a medication or refer for ambulatory monitoring.

Cardiology and stroke prevention. MAP and PP are tracked alongside systolic and diastolic in cardiology clinics, because both are independent predictors of cardiovascular events. A wide PP is associated with increased stroke risk; a low MAP is associated with peri-procedural complications.

Anaesthesia and critical care. MAP is the primary perfusion target in the operating room and the ICU. Vasopressors are titrated to maintain MAP above 65 mmHg in most septic-shock protocols; permissive hypotension targets a lower MAP in some trauma settings.

Obstetrics. Hypertensive disorders of pregnancy (gestational hypertension, pre-eclampsia, eclampsia) use absolute blood-pressure thresholds that differ from the AHA's adult categories. If you are pregnant, follow your obstetrician's thresholds, not this calculator.

Home monitoring. A 7-day log of twice-daily readings (morning and evening) is the standard input for ambulatory blood-pressure monitoring (ABPM) substitutes. Averaging reduces the white-coat effect (the inflation caused by being in a clinic) and the masked-hypertension effect (readings that are normal in clinic but high at home).

Pharmacy and community screening. Many community pharmacies offer walk-in blood-pressure checks. The category you are given at the pharmacy uses the same AHA / ACC 2017 bands as this calculator.

Common Mistakes

Using a single reading to diagnose hypertension. Blood pressure varies minute to minute. Guidelines require at least two readings on at least two separate occasions to diagnose hypertension outside the crisis range. The 7-day tracker tab helps you collect the second-occasion readings.

Talking during the reading. Talking raises systolic by 10 to 15 mmHg. Sit quietly for five minutes before measuring.

Crossing your legs. Crossing the legs at the knee raises systolic by 2 to 8 mmHg. Feet flat on the floor, back supported.

Cuff over clothing. A cuff over a sleeve can add 10 to 50 mmHg. Bare arm, cuff directly on the skin.

Cuff too small. A cuff that is too small for the arm circumference over-estimates systolic by 10 to 40 mmHg. The bladder should cover about 80% of the arm circumference.

Arm below heart level. Hanging the arm at the side over-estimates systolic by 10 to 15 mmHg. Rest the upper arm at heart level, about the level of the mid-sternum.

Empty bladder before measuring. A full bladder adds 10 to 15 mmHg. Empty bladder first.

Consuming caffeine, exercise, or smoking within 30 minutes. All three transiently raise systolic. Wait 30 minutes after any of them.

Rounding diastolic up to 80 or 90. A 129/85 reading is Stage 1, not high, because the diastolic is in the Stage 1 range. The AHA thresholds use "OR" between systolic and diastolic bands; check both.

Treating the calculator output as a diagnosis. This calculator is informational. A clinician, with access to your history, your medications, your ambulatory readings, and your other risk factors, makes the diagnosis.

Frequently Asked Questions

What does the AHA 2017 blood-pressure classification actually change?

It lowered the threshold for Stage 1 hypertension from 140/90 to 130/80. As a side effect, the share of US adults classified as hypertensive roughly doubled overnight (from about 30% to about 46%), although most of the newly-classified adults are recommended lifestyle changes first rather than medication. The five-band structure (Normal / high / Stage 1 / Stage 2 / Crisis) is unchanged from the older JNC 7 framework; only the cut-points shifted.

How is mean arterial pressure (MAP) calculated?

MAP = DBP + 0.4 × (SBP − DBP), which is algebraically equivalent to (2 × DBP + SBP) / 3. The 0.4/0.6 weighting reflects that the cardiac cycle spends more time in diastole than in systole. The formula assumes a healthy heart rhythm; in atrial fibrillation the true MAP varies beat-to-beat, and the figure should be treated as an average rather than a precise instantaneous value.

What is pulse pressure, and why does it matter?

Pulse pressure is SBP − DBP. A normal pulse pressure is roughly 40 mmHg (so 120/80 → PP 40). A wide pulse pressure (above 60 mmHg) in older adults suggests arterial stiffening from atherosclerosis or medial calcification and is an independent predictor of cardiovascular events. A narrow pulse pressure (below 25 mmHg) can suggest aortic stenosis, cardiac tamponade, or severe hypovolaemia. The calculator reports pulse pressure alongside the AHA category.

When should I be worried about a high reading?

A single reading above 180/120 mmHg is a hypertensive emergency if it is paired with chest pain, shortness of breath, vision changes, severe headache, or neurological symptoms. In that case, call emergency services. A single reading above 140/90 mmHg without warning symptoms is a reason to schedule a clinical evaluation within days, not hours. Two or more readings in the Stage 2 range on two separate occasions confirm a Stage 2 hypertension diagnosis.

What about low readings, when is hypotension a problem?

There is no formal AHA hypotension threshold for asymptomatic adults, but a systolic below 90 mmHg is a common clinical flag, and readings below 80 mmHg systolic can compromise organ perfusion. The calculator shows a low-systolic advisory when SBP is below 90. If low readings are paired with dizziness, fainting, fatigue, or cognitive fog, schedule a clinical evaluation. Many medications (especially antihypertensives, diuretics, and alpha-blockers) can over-treat and push readings too low.

Does the calculator account for arm-cuff size and technique?

No. The calculator is purely arithmetic. Measurement quality (cuff size, posture, rest period, talking, bladder state) can shift the reading by 10 to 50 mmHg. Follow a standardised home-measurement protocol: rest five minutes, sit with back supported, feet flat, legs uncrossed, arm at heart level, correct cuff size, no talking, bare arm. Take two readings one minute apart and average them.

Why does the AHA threshold differ from the older 140/90 cutoff?

The 2017 ACC/AHA committee concluded that the cardiovascular risk associated with systolic 130 to 139 (or diastolic 80 to 89) was high enough to warrant earlier intervention, particularly in patients with high 10-year cardiovascular risk. The lower threshold also aligns with the SPRINT trial, which found that targeting systolic below 120 (rather than below 140) reduced cardiovascular events by 25%. The European Society of Cardiology still uses 140/90 as its hypertension threshold, and NICE in the UK uses 140/90 for diagnosis and 150/90 for treatment in low-risk adults. If your clinician uses a different threshold, follow your clinician.

Can I use this calculator to titrate medication?

No. Titration requires multiple readings across days and weeks, knowledge of your other medications, your kidney function, your heart rate, and your side-effect profile. Use this calculator to track and understand trends; let your clinician titrate the medication.

Is the 7-day average the same as ambulatory blood-pressure monitoring (ABPM)?

No. ABPM uses a programmed cuff that takes readings every 15 to 30 minutes over 24 hours, including during sleep. The 7-day tracker in this calculator is a manual log, useful, but not a substitute for ABPM when a clinician suspects white-coat hypertension (high in clinic, normal at home) or masked hypertension (normal in clinic, high at home).

How do I convert mmHg to kPa and cmH₂O?

1 mmHg ≈ 0.13332 kPa (NIST Special Publication 811). 1 mmHg = 1.3595 cmH₂O (clinical convention). The convert-units tab handles both directions, with the two non-mmHg fields updating as soon as you finish typing in any of the three.

What is the difference between the optional age / sex risk bucket and a clinical cardiovascular risk score?

The age / sex bucket is informational only, it is a coarse label (low / moderate / high) that combines the AHA category with a simple age and sex modifier. It is not a quantitative risk score. Real cardiovascular risk scores (Framingham, ASCVD, SCORE2, QRISK3) require cholesterol, blood-glucose, smoking, and family-history inputs and produce a 10-year percentage risk. Use those calculators for actual risk estimates; use this one for tracking and category classification.

References

• Whelton, P. K., Carey, R. M., Aronow, W. S., et al. (2018). 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. Journal of the American College of Cardiology, 71(19), e127-e248. The foundational reference for the five-band classification used in this calculator.
• World Health Organization. Cardiovascular disease risk working group: technical package. WHO/NMH/PND/18.1. Provides the population-level blood-pressure targets used in global screening programmes.
• National Institute for Health and Care Excellence (NICE). Hypertension in adults: diagnosis and management (CG127, NG136). UK clinical guideline; uses a 140/90 threshold with ambulatory confirmation.
• Williams, B., Mancia, G., Spiering, W., et al. (2018). 2018 ESC/ESH Guidelines for the management of arterial hypertension. European Heart Journal, 39(33), 3021 to 3104. European threshold and treatment guidance.
• SPRINT Research Group. (2015). A randomized trial of intensive versus standard blood-pressure control. New England Journal of Medicine, 373(22), 2103 to 2116. The trial that informed the 2017 ACC/AHA systolic target.
• For the Blood Pressure Calculator, National Institute of Standards and Technology. NIST Special Publication 811: Guide for the Use of the International System of Units (SI). Source for the mmHg ↔ kPa conversion factor (1 mmHg = 133.322387415 Pa).