Blood pressure is considered to be high when the systolic reading is between 140 and 159 mm Hg or the diastolic reading is between 90 and 99 mm Hg or higher, according to the American Heart Association. This is known as stage 1 hypertension. A systolic reading of 160 mm Hg or higher, or a diastolic reading of 100 mm Hg or higher, is known as stage 2 hypertension.
A systolic reading higher than 180 mm Hg or a diastolic reading of higher than 110 mm Hg is considered a hypertensive crisis, for which emergency medical attention should be sought.
A normal blood pressure has a systolic reading lower than 120 mm Hg and a diastolic reading lower than 80 mm Hg, as reported by the American Heart Association.