Blood Pressure: what’s the difference between systolic, the top number, and diastolic, the bottom number.

What is blood pressure?

“Blood pressure is a measurement of the force applied to the walls of the arteries as the heart pumps blood through the body. The pressure is determined by the force and amount of blood pumped, and the size and flexibility of the arteries.

Blood pressure is continually changing depending on activity, temperature, diet, emotional state, posture, physical state, and medication use.”1

What’s the difference between systolic (the top number) and diastolic (the bottom number)?

“Blood pressure readings are measured in millimeters of mercury (mmHg) and usually given as 2 numbers. For example, 110 over 70 (written as 110/70).

  • The top number is the systolic blood pressure reading. It represents the maximum pressure exerted when the heart contracts.
  • The bottom number is the diastolic blood pressure reading. It represents the pressure in the arteries when the heart is at rest.”1

OK, so what’s happening when I’m getting it read at the doctors office?

When having your blood pressure read (using a sphygmomanometer or blood pressure cuff and a stethoscope), as the pressure around the arm reduces and the level on the dial or mercury tube falls, the point at which the pulsing (the thump, thump you feel) is first heard (the thump, thump the recorder hears) is recorded.1 This is the systolic pressure and represents how much force is being applied to the artery walls, how much blood is being pumped and how big & flexible your artery walls are when your under stress.

“As the air continues to be let out of the cuff, the sounds will disappear. The point at which the sound disappears is recorded. This is the diastolic pressure (the lowest amount of pressure in the arteries as the heart rests).”1

What’s a normal reading?

“In adults, the systolic pressure should be less than 120 mmHg and the diastolic pressure should be less than 80 mmHg.”1

Where can I learn more?

To learn more about risks of high & low blood pressure as well as what abnormal blood pressure readings are, visit this site: .

This post was quoted and summarized with permission from

1. Van Voorhees, Benjamin W., The University of Chicago, Chicago, IL. Review provided by VeriMed Healthcare Network.; ADAM Health Illustrated Encyclopedia,, 07/21/2006