Blood pressure is always measured on a number of different days and when you are at rest. If several of these measurements are too high, you are said to have high blood pressure, even if only one of the two – either the systolic or the diastolic one – is high. The medical term for high blood pressure is hypertension. In adults, blood pressure is considered to be normal under a systolic value of 140 mmHg and under a diastolic value of 90 mmHg.