Blood Pressure Calculator
Classify a reading under the current AHA/ACC framework, including the AND/OR logic that most tools get wrong.
Blood Pressure Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- A single reading cannot diagnose hypertension; repeated out-of-office measurement is required.
- Categories apply to untreated adults and are interpreted differently on medication.
- Does not account for age, pregnancy, or conditions that change target thresholds.
In short: A reading of 128/84 mm Hg is Stage 1 hypertension — not because of the systolic, which is merely elevated, but because the diastolic of 84 crosses the 80 mm Hg line. The higher of the two categories always governs.
Formula
The ANDs and the ORs are not decoration. Normal requires both numbers to qualify; hypertension requires only one.
Worked Example
- Read the systolic alone. 128 mm Hg falls in the elevated range — 120 to 129.
- Read the diastolic alone. 84 mm Hg falls in the stage 1 range — 80 to 89.
- Apply the OR rule. Stage 1 is SBP 130–139 OR DBP 80–89. The diastolic qualifies on its own.
- Take the higher category. The reading is Stage 1 hypertension, governed by the diastolic.
- Compute the derived measures. MAP is 84 + 44÷3 = 98.7 mm Hg; pulse pressure is 44 mm Hg.
The comparison field defaults to 118/82 for a reason. That reading has a systolic almost anyone would call excellent, and it is Stage 1 hypertension — because the classification uses OR for the hypertension stages and AND only for normal. A great many consumer tools, and a great many people reading their own home monitor, look at the top number, see 118, and stop. The diastolic of 82 is doing the work. The rule is worth memorising in the form that actually matters: to be normal you need both numbers under the line, but to be hypertensive you only need one of them over it.
Strengths & Limits Of This Model
Where this engine is strong
- Implements the AND/OR classification logic exactly as specified.
- Names which of the two numbers governs the category.
- Computes mean arterial pressure and pulse pressure with reference ranges.
Where it stops
- Cannot assess overall cardiovascular risk, which determines treatment.
- Cannot distinguish white-coat or masked hypertension from sustained hypertension.
Practical Use Cases
Classifying a home monitor reading
Check both numbers separately, then take the higher category. A single reading classifies nothing on its own.
Understanding why a good systolic is not enough
118/82 is Stage 1. The diastolic crosses the line on its own under the OR rule.
Tracking progress toward normal
Each of weight loss, sodium reduction, exercise and reduced alcohol moves systolic by roughly 4 to 5 mm Hg. Model the weight side with the Weight Loss Calculator.
Interpreting a wide pulse pressure
Above 60 mm Hg suggests arterial stiffening. Pair with the Resting Heart Rate Calculator for the broader cardiovascular picture.
Methodology & Editorial Standards
Blood pressure is classified under the current AHA/ACC four-category framework, and the engine implements its conditional logic exactly rather than approximating it. Normal requires systolic below 120 AND diastolic below 80, with both conditions necessary; elevated is systolic 120 to 129 AND diastolic below 80; stage 1 hypertension is systolic 130 to 139 OR diastolic 80 to 89; and stage 2 is systolic 140 or above OR diastolic 90 or above. The disjunction in the two hypertension stages is the part most consumer tools implement incorrectly, and the engine demonstrates it directly: a reading of 118 over 82 is stage 1 hypertension despite a systolic in the normal range, because only one of the two numbers needs to cross for the higher category to apply. The engine reports each number's band independently, names which one governs the overall classification, and computes mean arterial pressure as diastolic plus one third of pulse pressure, weighted that way because the cardiac cycle spends roughly two thirds of its duration in diastole. Pulse pressure is reported with the usual 40 to 60 mm Hg reference range, since a wide pulse pressure indicates reduced arterial compliance and is an independent risk marker in older adults. Measurement technique is emphasised because a single office reading is not diagnostic and confirmation normally requires out-of-office measurement. This calculator is an educational estimate and is not medical advice, diagnosis or treatment. Lipid and blood pressure values are interpreted in the context of overall cardiovascular risk, family history, diabetes, kidney function and medication, none of which a calculator can assess. Do not start, stop or change any medication on the basis of a figure produced here. Discuss results with a clinician, who will consider a full risk assessment rather than any single number. The engine implements the standard published formula for this calculation. Inputs are validated for domain and sign before evaluation, and any undefined case returns an em-dash rather than a spurious value.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Blood Pressure Calculator — 20 Expert FAQs
20 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Is 128/84 high blood pressure?
Yes, it is Stage 1 hypertension — driven by the diastolic of 84, since the systolic alone would be merely elevated.
What are the blood pressure categories?
Normal below 120/80, elevated 120–129 and under 80, stage 1 at 130–139 or 80–89, stage 2 at 140+ or 90+.
Why is 118/82 hypertension?
Because stage 1 uses OR, not AND. The diastolic of 82 crosses on its own, whatever the systolic reads.
Which number matters more?
Systolic predicts risk more strongly above about age 50; diastolic matters more in younger adults. Both are classified.
What is mean arterial pressure?
Diastolic plus one third of the pulse pressure — 98.7 mm Hg here. The usual range is 70 to 100.
What is pulse pressure?
Systolic minus diastolic, 44 mm Hg here. Above 60 suggests arterial stiffening; 40 to 60 is usual.
Does one high reading mean hypertension?
No. Diagnosis requires repeated readings, normally including out-of-office measurement, because white-coat hypertension is common.
How should I measure at home?
Sit quietly five minutes, back supported, feet flat, arm at heart height, no caffeine for thirty minutes. Average two readings.
What is a hypertensive crisis?
Systolic 180 or above, or diastolic 120 or above. Seek immediate care, urgently if there are symptoms.
How much can lifestyle lower blood pressure?
Weight loss, sodium reduction, exercise and less alcohol each move systolic by roughly 4 to 5 mm Hg, and they combine.
Does stage 1 hypertension need medication?
Often not immediately. Treatment depends on overall cardiovascular risk, and most stage 1 cases start with lifestyle change.
What is white-coat hypertension?
High readings in a clinical setting but normal outside it. It is why out-of-office confirmation is recommended.
What is masked hypertension?
The reverse — normal in clinic, high outside. It carries real risk and is missed by office measurement alone.
Does blood pressure vary through the day?
Considerably. It is typically lowest during sleep and rises before waking, which is why measurement timing should be consistent.
Can a narrow pulse pressure be a problem?
Below 40 mm Hg is often unremarkable alone, but with symptoms it can reflect reduced stroke volume and warrants attention.
Should I use the average of both arms?
Measure both initially and then use the arm with the higher reading consistently. A large difference between arms warrants review.
Is this blood pressure calculator free to use?
Yes. It is free, requires no account, and has no usage limits. ApexConverter is funded by contextual advertising, never by selling user data.
Is my data sent to a server?
No. The engine runs as Vanilla JavaScript inside your browser under our Zero-Server Client-Side Execution model. Your figures are computed locally and are never transmitted, logged, or stored.
How accurate is this calculator?
It applies the standard closed-form formula in IEEE-754 double precision, rounding only at the display layer. The engine is reconciled against an independent reference implementation before release.
Does it work on mobile?
Yes. The interface is mobile-first with numeric keypad hints and is tested down to a 320-pixel viewport with no horizontal scrolling.