When your doctor takes your blood pressure, it's expressed as a measurement with two numbers, with one number on top (systolic) and one on the bottom (diastolic), like a fraction. Blood pressure numbers of less than 120/80 mm Hg are considered within the normal range. Normal: Less than 120 millimeters of mercury (mm Hg) for systolic and 80 mm Hg for diastolic. The gauge uses a unit of measurement called millimeters of mercury (mmHg) to measure the pressure in your blood vessels. In adults, blood pressure is considered to be normal under a systolic value of 140 mmHg and under a diastolic value of 90 mmHg.