How to read your blood pressure and understand what it means for you

• Blood pressure readings are a measurement of two numbers: systolic and diastolic.
• These two numbers can tell you if your blood pressure is low, normal, elevated, high, or if you're having a hypertensive crisis (very high).
• Here's how to read your blood pressure measurements and understand what it means for you.
• This article was medically reviewed by John Osborne, MD, PhD, and the Director of Cardiology for Dallas-based State of the Heart Cardiology.

High blood pressure is known as the "silent killer" because it usually doesn't come with symptoms, and it can be dangerous if left untreated.

The only way to know your blood pressure and keep track of your heart health is through accurate readings and frequent measurements.

Here's what you need to know about your blood pressure reading and what it means for you.

Blood pressure readings

Blood pressure is the force of blood pushing against the arteries in your body. It is measured by two numbers:

• Systolic pressure (top number). The pressure exerted against your artery walls when your heart beats.
• Diastolic pressure (bottom number). The pressure exerted against your artery walls when your heart rests, in between beats.

Blood pressure is measured in millimeters of mercury (mm Hg). To determine whether someone has high blood pressure, known medically as hypertension, doctors classify blood pressure readings into different categories.

Normal blood pressure

Normal blood pressure is considered:

• Systolic: Lower than 120 mm Hg
• Diastolic: Lower than 80 mm Hg

If you have a blood pressure reading around this number, it generally means your heart is healthy. However, even if you have normal blood pressure, certain factors can increase your risk of developing hypertension over time.

These include:

• Smoking cigarettes
• Physical inactivity, or lack of exercise
• Obesity, or excess body fat
• Consuming too much salt
• Eating too little potassium
• Drinking too much alcohol
• Family history of hypertension

Low blood pressure

Sometimes, blood pressure can be lower than normal. Low blood pressure is considered:

• Systolic: Lower than 90 mm Hg
• Diastolic: Lower than 60 mm Hg

Low blood pressure isn't always cause for concern — in fact, it's often harmless, and can even indicate good health.

"If you're an athlete, an exerciser, or someone who does a lot of things to take care of their body, it can be normal to have a relatively low blood pressure," says Jordana Cohen, MD, a hypertension expert at Penn Medicine.

However, you should check in with your doctor when low blood pressure is accompanied by the following symptoms:

• Lightheadedness upon standing
• Dizziness
• Quick, shallow breathing
• Unusual thirst
• Nausea

This may be a result of certain conditions or medications. Low blood pressure typically occurs with Parkinson's disease, hormonal changes, and pregnancy.

Elevated blood pressure

Elevated blood pressure is considered:

• Systolic: 120 to 129 mm Hg
• Diastolic: Lower than 80 mm Hg

This is the first warning sign for hypertension — and it's often called pre-hypertension. Your doctor will talk with you about implementing lifestyle changes that can effectively lower blood pressure, including:

• Maintain a healthy weight
• Get more exercise
• Lower sodium intake
• Eat a more balanced diet
• Limit alcohol consumption
• Quit smoking
• Manage stress

Hypertension: Stage 1

Hypertension is considered:

• Systolic: 130 to 139 mm Hg
• Diastolic: 80 to 89 mm Hg

Medication is generally not considered necessary to treat hypertension at this level, and you should instead commit to making those healthier lifestyle choices to lower blood pressure, says Cohen.

If you have to focus your energy on one blood-pressure-reducing activity, Cohen recommends exercise, as it not only lowers blood pressure on its own, but it can also reduce stress, which is another cause of high blood pressure.

Hypertension: Stage 2

Hypertension becomes worse when it rises to:

• Systolic: more than 140 mm Hg
• Diastolic: more than 90 mm Hg

While intensive lifestyle modification to reduce high blood pressure is still necessary, Cohen says medication is also typically required to lower someone's stage 2 hypertension.

If left untreated, blood pressure this high can lead to the following health threats:

• Heart attack
• Heart failure
• Stroke
• Vision loss
• Sexual dysfunction
• Kidney disease or kidney failure

Hypertensive crisis

A hypertensive crisis is considered:

• Systolic: more than 180 mm Hg
• Diastolic: more than 120 mm Hg

This can be very dangerous and require immediate medical attention, especially if it's combined with the following symptoms:

• Shortness of breath
• Headache
• Nosebleed
• Severe anxiety
• Back pain
• Numbness
• Changes in vision

A hypertensive crisis can result in organ damage, and indicates a heightened risk for stroke, heart attack, and other life-threatening consequences. If you're experiencing blood pressure this high along with any of these symptoms, call 911 immediately.

How often should you measure blood pressure?

If you have normal blood pressure, and your doctor thinks you're at a low risk for developing hypertension, you'll likely only get your blood pressure measured once a year, at a routine check-up.

However, if you're at risk or have hypertension, your doctor may recommend that you check blood pressure at home.

If you have a clinician-approved at-home blood pressure measuring kit, you should measure your blood pressure twice in the morning and twice in the evening, waiting a minute between readings, says Cohen.

Additionally, she says it's important to calmly wait five minutes before measuring your blood pressure, as it can affect the accuracy of your reading.

"If you're checking your blood pressure when you're exercising, moving around, or without taking that five minute break, then it's just not a useful blood pressure," Cohen says.

Cohen recommends using a blood pressure measuring device from an accredited source, such as Validate BP. Devices are independently reviewed by experts associated with the American Heart Association to see which ones provide the best, clinically accurate results.

Related stories from Health Reference:

• Dark chocolate can be good for your heart, in moderation
• What is a silent heart attack? How to recognize the warning signs
• How hypertension, heart disease, and stroke are related
• How to lower blood pressure with a heart-healthy diet and exercise