Blood Pressure Calculator

The American Heart Association updated its blood pressure guidelines in 2017, lowering the threshold for hypertension from 140/90 to 130/80 mmHg.

Under the current framework:

• Normal blood pressure is below 120/80 mmHg.
• Elevated is systolic 120-129 with diastolic below 80 — a warning stage requiring lifestyle changes.
• Hypertension Stage 1 is systolic 130-139 or diastolic 80-89, where doctors consider medication if cardiovascular risk factors are present.
• Hypertension Stage 2 is systolic 140+ or diastolic 90+, typically requiring medication plus lifestyle modification.
• Hypertensive Crisis (systolic over 180 or diastolic over 120) demands immediate medical attention.

When systolic and diastolic readings fall into different categories, the higher category applies. For example, a reading of 138/78 is Stage 1 hypertension based on the systolic value alone.

These thresholds are based on large-scale studies showing that cardiovascular risk begins rising continuously above 115/75 mmHg.

Mean Arterial Pressure (MAP) is the weighted average pressure during one cardiac cycle, calculated as MAP = Diastolic + (Systolic − Diastolic) / 3. The formula weights diastolic more heavily because the heart spends roughly two-thirds of the cycle in relaxation.

A normal MAP ranges from 70 to 100 mmHg. Below 60 mmHg, vital organs may not receive adequate blood flow — a critical threshold in emergency medicine and ICU monitoring. Above 100 mmHg indicates the heart is working harder than normal, increasing risk of organ damage over time.

Pulse pressure — the difference between systolic and diastolic — is another important derived metric. Normal pulse pressure is 30-40 mmHg. A widened pulse pressure above 60 mmHg can indicate aortic stiffness, aortic regurgitation, or hyperthyroidism. A narrow pulse pressure below 25 mmHg may suggest heart failure or significant blood loss.

Together, MAP and pulse pressure provide a more complete hemodynamic picture than systolic and diastolic values alone.

Home blood pressure monitoring is recommended by the AHA for anyone with elevated readings, but technique errors can produce readings that are 10-20 mmHg off.

• First, use an upper-arm cuff validated by the Association for the Advancement of Medical Instrumentation (AAMI) — wrist and finger monitors are less accurate.
• Second, sit quietly for 5 minutes before measuring, with your back supported, feet flat on the floor, and arm resting on a table at heart level. Crossing legs can raise systolic pressure by 2-8 mmHg.
• Third, avoid caffeine, exercise, and smoking for 30 minutes beforehand.
• Fourth, take two readings one minute apart and average them — single readings can vary significantly.
• Fifth, measure at the same times daily (morning before medication and evening) to establish a reliable trend.

White coat hypertension (elevated readings only at the doctor) affects 15-30% of patients, while masked hypertension (normal at the doctor but elevated at home) affects about 10%. Regular home monitoring catches both patterns and gives your physician a far more accurate picture.

A blood pressure reading has two numbers written as systolic over diastolic, for example 120/80 mmHg.

Systolic (the top number) is the pressure when the heart beats; diastolic (the bottom) is the pressure when the heart rests between beats. Both matter, and either being high can indicate hypertension.

The American Heart Association classifies readings using both values, so this calculator interprets the pair together rather than either number alone.

Under the AHA's 2017 guidelines, normal blood pressure is below 120/80 mmHg.

• 'Elevated' is 120-129 systolic and under 80 diastolic.
• Stage 1 hypertension is 130-139 or 80-89.
• Stage 2 is 140/90 or higher.
• A reading above 180/120 is a hypertensive crisis needing urgent care.

These thresholds apply to most adults, though individual targets can differ, so discuss your ideal range with a clinician — especially if you have diabetes or kidney disease.

High blood pressure often has no symptoms, which is why the CDC calls it a 'silent killer.' Sustained hypertension damages arteries and raises the risk of heart attack, stroke, heart failure, and kidney disease.

Contributing factors include:

• age
• family history
• high sodium intake
• excess weight
• inactivity
• alcohol
• stress

Because it is usually symptomless, regular measurement is the only way to detect it, and treatment combines lifestyle changes with medication when needed.

Blood pressure that is too low — generally under 90/60 mmHg — can cause dizziness, fainting, blurred vision, and fatigue, especially on standing (orthostatic hypotension).

Causes include:

• dehydration
• blood loss
• certain medications
• endocrine problems

For many people a naturally low reading is harmless, and when mild dehydration is the cause our water intake calculator can help you set a realistic daily fluid target, though symptomatic hypotension still warrants medical evaluation. The Mayo Clinic advises seeking care if low readings come with fainting or confusion, which can signal an underlying condition.

Two derived numbers add insight.

Pulse pressure is systolic minus diastolic (e.g., 120−80 = 40); a widening pulse pressure with age can reflect arterial stiffening.

Mean arterial pressure (MAP) estimates the average pressure driving blood to organs and is clinically important in critical care.

This calculator reports both, but they supplement — not replace — the standard category based on the systolic and diastolic readings.

Evidence-based steps can meaningfully reduce blood pressure. The NIH-developed DASH diet (rich in fruits, vegetables, whole grains, and low-fat dairy, low in sodium) can lower systolic pressure by several points.

Reducing sodium, losing excess weight, exercising regularly, limiting alcohol, quitting smoking, and managing stress all help.

The AHA recommends these changes as first-line for elevated and Stage 1 hypertension, often alongside medication for higher readings, under medical supervision.

A single high reading isn't a diagnosis — blood pressure varies through the day.

But readings consistently at or above 130/80, or any reading above 180/120, warrant medical attention; the latter, especially with chest pain, shortness of breath, or vision changes, is a hypertensive emergency requiring immediate care.

This calculator is an educational tool, not a diagnosis; use it to track trends and share readings with your healthcare provider.

Inaccurate technique skews readings.

Common mistakes include:

• measuring right after caffeine, exercise, or a stressful moment
• a full bladder
• talking during measurement
• wrong cuff size
• crossed legs
• an unsupported arm

The AHA advises sitting quietly for five minutes, feet flat, arm at heart level, and taking two readings a minute apart. Home monitoring is valuable for spotting trends, but only with correct technique and a validated, properly sized cuff.