Blood Pressure Numbers Explained: What Is Normal, Elevated or High?

A blood pressure reading is written as two numbers, such as 120/80. Many people know the numbers matter but are unsure what counts as normal. This article explains the numbers using the CDC, NHS and WHO. Remember that only a health professional can tell you what your own readings mean.

What the two numbers mean

Blood pressure is measured in millimetres of mercury, written mm Hg. The first, higher number is the systolic pressure, and the second is the diastolic pressure. The CDC describes blood pressure as the force of blood against the walls of the arteries. A cuff around the upper arm is used to measure it, according to the NHS.

Categories from the CDC

The CDC groups readings like this:

• Normal: systolic below 120 and diastolic below 80
• Elevated: systolic 120 to 129 and diastolic below 80
• High: systolic 130 or higher, or diastolic 80 or higher

The CDC describes high blood pressure as pressure that is consistently at or above 130/80.

What the NHS and WHO say

Other health bodies use somewhat different cut-offs for diagnosis. The NHS says high blood pressure is usually 140/90 or higher when measured by a professional, or 135/85 or higher when measured at home. The WHO defines hypertension as 140/90 mm Hg or higher, and says the diagnosis needs readings at or above that level on two different days.

The WHO also describes treatment goals. It says the goal is below 130/80 for people with cardiovascular disease, diabetes, chronic kidney disease or high cardiovascular risk, and below 140/90 for most other people. Because targets depend on your own health, your doctor will tell you the target that applies to you.

Why readings can differ

The NHS explains that blood pressure varies through the day and is affected by activity and how you feel. This is why one reading is not enough. If a high reading is suspected, the NHS says you may be asked to take readings at home for several days, return for another check, or wear a monitor that records readings for 24 hours.

What about low blood pressure?

The NHS describes low blood pressure as a reading of less than 90/60 mm Hg. It does not always cause symptoms. When it does, they can include dizziness or light-headedness, nausea, blurred vision, weakness, confusion and fainting. The NHS says causes include being fit and healthy, inheriting low blood pressure, ageing, pregnancy, medical conditions such as diabetes and certain medicines. Treatment is rarely needed, and a doctor will look for a cause if you keep having symptoms.

Taking readings at home

The WHO says people can use automated home devices, but a professional evaluation is still needed to assess overall risk. Keep a record of your readings and take it to your appointments. Do not change prescribed medicine because of a single reading.

When to see a doctor

See a doctor to have your blood pressure measured if you have not had it checked recently, if you are at higher risk, or if your home readings are often above the levels your doctor gave you. The NHS advises seeing a doctor if you keep getting dizziness or fainting. Seek urgent help for a very high reading with severe headache, chest pain, confusion or vision changes, as the WHO describes.

Call emergency services immediately for sudden chest pain that does not go away, or chest pain with sweating, sickness, light-headedness or breathlessness. Do not drive yourself to hospital.

In an emergency, call your local emergency number (112 in India, 911 in the United States).