Blood pressure is measured as two numbers: systolic (pressure when the heart beats) over diastolic (pressure between beats), expressed in mmHg. Normal blood pressure is under 120/80 mmHg. A reading of 125/82 falls in the "Elevated" category; 145/92 is "Stage 2 Hypertension." The two numbers together tell your doctor about the condition of your cardiovascular system and immediate pumping health of the heart.
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What Is Blood Pressure?
Blood pressure is the force that your blood exerts against the walls of your arteries as your heart pumps it through your body. It is measured as two numbers expressed in millimeters of mercury (mmHg): systolic pressure (the higher number) over diastolic pressure (the lower number). Systolic pressure measures the force when your heart contracts and pushes blood out; diastolic pressure measures the force when your heart relaxes between beats.
A blood pressure reading of 120/80 mmHg is considered normal — the systolic is 120 and the diastolic is 80. Both numbers matter. You can have elevated systolic with normal diastolic, normal systolic with elevated diastolic, or both elevated. The American Heart Association's 2017 guidelines define five categories: Normal (under 120/80), Elevated (120–129/under 80), Hypertension Stage 1 (130–139/80–89), Hypertension Stage 2 (140+/90+), and Hypertensive Crisis (180+/120+).
High blood pressure, known as hypertension, affects nearly half of all American adults and is often called the "silent killer" because it typically produces no symptoms until serious cardiovascular damage has already occurred. Over time, uncontrolled high blood pressure damages arteries, strains the heart, and dramatically increases the risk of heart attack, stroke, kidney disease, and heart failure. Understanding your blood pressure numbers, what category they fall in, and what that means for your health is the most important first step toward protecting your cardiovascular system.
Understanding Blood Pressure Readings
Systolic pressure (top number): The maximum pressure in your arteries when your heart contracts and pumps blood. A healthy systolic is under 120 mmHg.
Diastolic pressure (bottom number): The minimum pressure in your arteries between heartbeats when the heart is relaxing. A healthy diastolic is under 80 mmHg.
The American Heart Association Blood Pressure Categories (2017 guidelines):
| Category | Systolic (mmHg) | | Diastolic (mmHg) | |----------|--------------|---|-----------------| | Normal | Under 120 | and | Under 80 | | Elevated | 120–129 | and | Under 80 | | Hypertension Stage 1 | 130–139 | or | 80–89 | | Hypertension Stage 2 | 140+ | or | 90+ | | Hypertensive Crisis | 180+ | and/or | 120+ |
Hypertensive Crisis requires immediate medical attention. Seek emergency care if your reading is above 180/120 mmHg, especially with symptoms like severe headache, chest pain, or vision changes.
Low Blood Pressure (Hypotension): Generally under 90/60 mmHg. Low blood pressure becomes concerning when it causes dizziness, fainting, or lightheadedness. Causes include dehydration, prolonged bed rest, certain medications, heart problems, or endocrine disorders.
What Causes High Blood Pressure?
Primary (essential) hypertension: 90–95% of cases. No single identified cause; develops gradually over years. Risk factors include: age (stiffening arteries), genetics, obesity, high-sodium diet, physical inactivity, tobacco use, excessive alcohol, chronic stress, chronic kidney disease, and sleep apnea.
Secondary hypertension: 5–10% of cases. Caused by an underlying condition: kidney disease, adrenal gland tumors, thyroid disorders, certain medications (birth control pills, cold medications, NSAIDs), or illegal drugs.
How to Accurately Measure Blood Pressure at Home
Home monitoring is valuable but requires correct technique for accurate readings:
- Avoid caffeine, exercise, and smoking for 30 minutes before measuring.
- Sit quietly for 5 minutes before taking a reading. Stress and activity elevate blood pressure significantly.
- Use the correct cuff size. A cuff too small gives falsely high readings; too large gives falsely low readings. The inflatable part should encircle at least 80% of the upper arm.
- Sit with back supported, feet flat, arm at heart level.
- Take two to three readings, 1–2 minutes apart, and average them.
- Measure at the same time each day — blood pressure naturally varies throughout the day (lowest in the morning, higher in the afternoon and evening).
"White coat hypertension" — elevated readings in medical settings due to anxiety — is common. Home monitoring over time gives a more accurate picture of true blood pressure than isolated clinic readings.
Frequently Asked Questions
Can diet significantly lower blood pressure? Yes. The DASH diet (Dietary Approaches to Stop Hypertension) can reduce systolic blood pressure by 8–14 mmHg — equivalent to many medications. Key changes: reduce sodium to under 2,300 mg/day (ideally 1,500 mg); increase potassium (bananas, leafy greens, sweet potatoes); reduce saturated fat; increase fruits, vegetables, and whole grains; limit alcohol to 1 drink/day for women, 2 for men. These changes together produce meaningful reductions in 2–4 weeks.
How much does exercise lower blood pressure? Regular aerobic exercise (30 minutes/day most days) can reduce systolic blood pressure by 4–9 mmHg in people with hypertension. The effect begins within a few weeks of starting regular exercise. The impact is most significant in Stage 1 hypertension and may be sufficient to avoid or delay medication. Resistance training (strength training) also lowers blood pressure but less so than aerobic exercise.
What is pulse pressure and why does it matter? Pulse pressure = systolic − diastolic. Normal pulse pressure is 40 mmHg (e.g., 120/80). High pulse pressure (>60 mmHg) in older adults indicates arterial stiffness and is an independent predictor of cardiovascular disease risk — separate from hypertension. A reading of 160/90 has a pulse pressure of 70, which raises concern beyond just the elevated readings alone.
At what blood pressure level should I take medication? Current guidelines (American Heart Association): Medication is typically recommended for Stage 1 hypertension (130–139/80–89) if the patient has high cardiovascular risk (prior heart attack, stroke, or high 10-year cardiovascular risk score). For lower-risk individuals at Stage 1, lifestyle changes alone for 3–6 months are recommended first. Stage 2 hypertension (140+/90+) typically requires medication plus lifestyle changes. The decision is individualized — work with your healthcare provider.
Is it normal for blood pressure to vary throughout the day? Yes. Blood pressure follows a circadian rhythm: it is typically lowest during sleep, rises sharply in the morning ("morning surge"), and gradually increases through the day before falling in the evening. It also temporarily increases with physical activity, stress, caffeine, and cold temperatures. A single elevated reading does not diagnose hypertension — the diagnosis requires consistently elevated readings across multiple measurements on multiple occasions.
Related Free Tools on RoughTools
- Heart Rate Calculator — calculate heart rate zones alongside blood pressure monitoring
- BMI Calculator — BMI reduction is correlated with blood pressure improvement
- Calorie Calculator — weight management through caloric awareness
- Water Intake Calculator — adequate hydration supports normal blood pressure
Interpret Your Blood Pressure Reading Now
Use the free Blood Pressure Interpreter at RoughTools to see which category your reading falls in, understand what it means for your health, and get personalized guidance for improving or maintaining your numbers. No account needed, completely free.