Blood pressure is the pumping action of the heart the force of blood pushing against the walls of the arteries as the heart pumps blood. Differences in mean blood pressure are responsible for blood flow from one location to another in the circulation. The rate of mean blood flow depends on the resistance to flow presented by the blood vessels. Mean blood pressure decreases as the circulating blood moves away from the heart through arteries and capillaries due to viscous losses of energy. Mean blood pressure drops over the whole circulation, although most of the fall occurs along the small arteries and arterioles.
Knowing your blood pressure numbers is important, even when you're feeling fine. If your blood pressure is normal, you can work with your health care team to keep it that way. If your blood pressure is too high, treatment may help prevent damage to your body's organs.
Blood Pressure Numbers
Blood pressure is measured as systolic (sis-TOL-ik) and diastolic (di-ah-STOL-ik) pressures. "Systolic" refers to blood pressure when the heart beats while pumping blood. "Diastolic" refers to blood pressure when the heart is at rest between beats.
You most often will see blood pressure numbers written with the systolic number above or before the diastolic number, such as 120/80 mmHg. (The mmHg is millimeters of mercury—the units used to measure blood pressure.)
The table below shows normal blood pressure numbers for adults. It also shows which numbers put you at greater risk for health problems.
| Category | Systolic | Diastolic | |
| (top number) | (bottom number) | ||
| Normal | Less than 120 | And | Less than 80 |
| Prehypertension | 120–139 | Or | 80–89 |
| High blood pressure | |||
| Stage 1 | 140–159 | Or | 90–99 |
| Stage 2 | 160 or higher | Or | 100 or higher |
The ranges in the table apply to most adults (aged 18 and older) who don't have short-term serious illnesses.
Blood pressure doesn't stay the same all the time. It lowers as you sleep and rises when you wake up. Blood pressure also rises when you're excited, nervous, or active. If your numbers stay above normal most of the time, you're at risk for health problems. The risk grows as blood pressure numbers rise. "Prehypertension" means you may end up with HBP, unless you take steps to prevent it.
If you're being treated for HBP and have repeat readings in the normal range, your blood pressure is under control. However, you still have the condition. You should see your doctor and follow your treatment plan to keep your blood pressure under control.
Your systolic and diastolic numbers may not be in the same blood pressure category. In this case, the more severe category is the one you're in. For example, if your systolic number is 160 and your diastolic number is 80, you have stage 2 HBP. If your systolic number is 120 and your diastolic number is 95, you have stage 1 HBP.
