In adults, a normal blood pressure reading is less than 120/80 millimeters of mercury, states the American Heart Association. This measurement records systolic blood pressure, the force of blood on the arteries when the heart pumps blood, and diastolic blood pressure, the force of blood when the heart is resting.
Blood pressure changes in response to emotional stress, physical activity, sleep and changes in posture, explains the American Heart Association. A person with consistently elevated blood pressure may need to alter their eating habits, get more exercise or take medications to control the condition. Adults should have their blood pressure checked every two years once they reach the age of 20, but more frequent checks are necessary in people who have been diagnosed with high blood pressure.