Your body controls your blood pressure in many ways, how hard and fast the heart pumps, how much your blood vessels tighten and through your kidneys. The pressure will vary at different times of the day and in different circumstances. Once sitting down in a quiet environment, your resting blood pressure should be below 140mmHg / 90mmHg. If you have specific medical conditions such as diabetes, stroke, heart disease or kidney disease, this reading should be even lower.
The only way most people know if their blood pressure is high is to measure it with a properly calibrated blood pressure machine called a digital sphigmomanometer (or manual version). Blood pressure should be checked regularly if you have a condition that increases your risk of cardiovascular disease. If you are healthy and well, it’s best to have your blood pressure checked opportunistically each year.