What Is Blood Pressure?
Blood pressure is the force that your blood exerts against the walls of your arteries as your heart pumps it around your body. It's one of the most important vital signs — and one of the most commonly misunderstood. A blood pressure reading consists of two numbers, and both matter.
Breaking Down the Numbers
A reading is written as two figures separated by a slash, such as 120/80 mmHg. Here's what each number means:
- Systolic pressure (top number): The pressure in your arteries when your heart beats and pumps blood out.
- Diastolic pressure (bottom number): The pressure in your arteries when your heart rests between beats.
Both numbers are measured in millimeters of mercury (mmHg).
Blood Pressure Categories at a Glance
Medical organizations generally classify blood pressure into the following ranges for adults:
| Category | Systolic (mmHg) | Diastolic (mmHg) |
|---|---|---|
| Normal | Less than 120 | Less than 80 |
| Elevated | 120–129 | Less than 80 |
| High (Stage 1) | 130–139 | 80–89 |
| High (Stage 2) | 140 or higher | 90 or higher |
| Hypertensive Crisis | Higher than 180 | Higher than 120 |
| Low (Hypotension) | Less than 90 | Less than 60 |
Note: These ranges apply to most adults. Your doctor may interpret your readings differently based on your age, health history, and other factors.
Why Does High Blood Pressure Matter?
Hypertension (high blood pressure) is often called the "silent killer" because it rarely causes noticeable symptoms in its early stages. Over time, untreated high blood pressure can damage blood vessels and increase the risk of:
- Heart attack and coronary artery disease
- Stroke
- Heart failure
- Kidney damage
- Vision loss
Factors That Affect Blood Pressure Readings
Blood pressure is dynamic — it fluctuates throughout the day based on many factors, including:
- Physical activity and exercise
- Stress, anxiety, or emotional state
- Caffeine and alcohol intake
- Recent meals
- Time of day (typically lower at night)
- Whether you were sitting or standing when measured
For this reason, a single reading should not be used alone to diagnose high blood pressure. Clinicians typically look at readings taken on multiple occasions.
How to Get an Accurate Reading at Home
- Sit quietly for five minutes before measuring.
- Avoid caffeine, exercise, and smoking for at least 30 minutes beforehand.
- Sit with your back supported and feet flat on the floor.
- Rest your arm on a flat surface at heart level.
- Take two or three readings, one minute apart, and record the average.
- Measure at the same time each day for consistency.
When to Speak to Your Doctor
You should contact your healthcare provider if your readings are consistently at or above 130/80 mmHg, or if you experience symptoms such as severe headaches, nosebleeds, chest pain, or sudden vision changes alongside elevated readings. A hypertensive crisis reading above 180/120 mmHg requires immediate medical attention.
Regular monitoring and open communication with your doctor are the most effective tools for managing blood pressure and protecting your long-term health.