A blood pressure measurement determines the force of blood against your artery walls as it's pumped by your heart. When the force is too strong over a prolonged period of time, as in the case of someone with high blood pressure, it can damage your heart, blood vessels and kidneys.
Your blood pressure measurement includes two numbers. The systolic number, which is the top or first number, measures the pressure when your heart is beating, while the dystolic number, the bottom or second number, measures the pressure when your heart is at rest.
A normal blood pressure measures 120 millimeters or less over 80 millimeters or less. High blood pressure measures 140 millimeters or greater over 90 millimeters or greater. Only your doctor can determine if you have high blood pressure.