Normal blood pressure is around 120/80 mmHg (120: systolic blood pressure, 80: diastolic blood pressure). Blood pressure readings lower than 90 mmHg (systolic) or 60 mmHg (diastolic) are usually considered low blood pressure. Causes of low blood pressure can range from dehydration to serious medical disorders. It is important to find out what is causing your low blood pressure so that it can be treated.