High Blood Pressure: Understanding Blood Pressure (BP) Readings

How is blood pressure measured? And what does systolic and diastolic pressure mean? Cardiologist Associate Professor Calvin Chin from the National Heart Centre Singapore explains.

What is Blood Pressure?

Blood pressure refers to the force of the body’s blood pushing against the inner walls of the blood vessels, especially the arteries. Each time the heart contracts, it pumps blood into the arteries. Your blood pressure doesn’t stay constant throughout the day. It is lowest when you’re sleeping, and rises when you get up and start moving about. It can also go up when you are excited, nervous or physically active.

What is Systolic and Diastolic Blood Pressure?

Systolic pressure refers to the blood pressure in the arteries that results when your heart contracts or beats, pushing blood out. When your heart relaxes between beats, blood pressure in the arteries falls. This is the diastolic pressure. Diastolic blood pressure can increase with age as a result of stiffening arteries.

Blood Pressure Readings: What's Normal and When is it High Blood Pressure?

Blood pressure (BP) readings are expressed as a ratio of the systolic pressure (the first number or numerator), over the diastolic pressure (the second number or denominator). A blood pressure of 120/80 mmHg (millimetres of mercury) is expressed verbally as 120 over 80.

A healthy blood pressure reading should be lower than 120/80 mmHg. Normal blood pressure is less than 120 mmHg systolic and 80 mmHg diastolic (see blood pressure chart below), and may vary from 90/60 mmHg to 120/80 mmHg in a healthy young woman. A blood pressure of 140/90 mmHg or higher indicates high blood pressure.

Categories for Blood Pressure Levels in Adults (Aged 18 Years and Older)

​ ​ ​

​ ​ Blood Pressure Level (mmHg)




Normal BP​

< 120


< 80

High-Normal BP



80 - 89

High Blood Pressure​

Stage 1 Hypertension

140 - 159


90 - 99

Stage 2 Hypertension




* Isolated Systolic Hypertension

> 140


< 90


1. When systolic and diastolic blood pressures fall into different categories, the higher category should be used to classify blood pressure level. For example, 160/80 mmHg would be stage 2 hypertension (high blood pressure).

2. *Isolated systolic hypertension is graded according to the same level of systolic BP.

Measuring Blood Pressure at Home

You can measure your own blood pressure at home with a digital blood pressure device that can be purchased at most pharmacies. Read the instructions carefully. You may wish to calibrate your reading with your family doctor. The right time to take the measurement is when you are at rest.

Some tips that will help ensure the accuracy of your blood pressure reading include:

• Sitting in a comfortable position

• Placing your left arm, raised to the level of your heart, on a table or desk, and sit still

• Wrapping the cuff of the monitor smoothly and snugly around the upper part of your bare arm

Fun Facts About Blood Pressure Readings

Researchers from the Center for Health Research and Rural Advocacy at Geisinger Health System in Pennsylvania have found that time of day and time of year can influence blood pressure readings by as much as 40 percent.

In addition, blood pressure also fluctuates with physical activity and emotional state. It may help make your results more comparable if you measure your blood pressure at the same time every day, under resting conditions and on more than one occasion.

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