How to Measure Blood Pressure at Home Accurately: A Step-by-Step Guide

Why technique changes the number

Blood pressure is the force of blood against the walls of the arteries, and the National Heart, Lung, and Blood Institute describes it with two numbers. Systolic pressure, the top number, is the pressure when the heart beats. Diastolic pressure, the bottom number, is the pressure when the heart rests between beats. Both are measured in millimeters of mercury, written mmHg.

Neither number is a fixed property of a person. Pressure moves from minute to minute with posture, talking, a full bladder, caffeine, nicotine, cold, pain and stress. That is not a flaw in the measurement. It is what blood pressure does, and it is why guidelines specify a measurement routine: a reading taken under standard conditions can be compared with one taken another day and with the thresholds that guidelines set.

Home measurement has become more common because a single reading in a clinic is only a snapshot, and some people’s pressure rises in a medical setting. A set of readings taken calmly at home gives a clinician more to work with. That value depends entirely on the readings being taken properly.

Home monitoring suits some people better than others. It is commonly used by people who have been diagnosed with high blood pressure and want to see how it behaves day to day, by people whose clinic readings differ from what is expected, and by people whose clinician has asked for a log. It is not a substitute for regular check-ups, and a normal home reading does not mean other measurements can be skipped.

Before you measure

Most of the avoidable error in home readings happens in the minutes before the cuff goes on. The American Heart Association’s guidance gives a short list of things to do and to avoid.

• Do not smoke, exercise, or drink caffeinated beverages or alcohol in the 30 minutes before you measure.
• Sit still in a chair for five minutes first, without talking or moving about.
• Consider emptying your bladder beforehand, since a full bladder can raise a reading slightly.
• Use the same arm each time and, where you can, measure at the same times of day so readings are comparable.

Position the body and the cuff

Posture is where many home readings go wrong. A reading taken with the legs crossed, the back unsupported or the arm hanging below the heart will differ from one taken correctly, and not in a way you can predict.

1. Sit upright in a chair with your back supported and your feet flat on the floor, legs uncrossed.
2. Rest the cuffed arm on a flat surface such as a table, so the cuff sits at the level of your heart.
3. Wrap the cuff on bare skin, not over clothing, just above the bend of the elbow, following the instructions that came with the monitor.
4. Stay relaxed and do not talk while the monitor is measuring.
5. Read or record the result once the monitor finishes. Do not squeeze or re-inflate the cuff to check.

The reason for the instruction is that arm position changes the reading, which is why the guidance specifies heart level. A table or armrest makes it easy to get right.

Choosing the right cuff size

Cuff size is an easily overlooked source of error. The American Heart Association’s guidance advises making sure the cuff is the right size, and a cuff of the wrong size gives an inaccurate reading. Monitors come with a stated range of arm circumferences they are designed for.

• Measure the circumference of your upper arm, halfway between shoulder and elbow, with a flexible tape.
• Check that measurement against the size range printed on the monitor or its packaging.
• If you are between sizes, or outside the standard range, look for a monitor that comes with a larger or smaller cuff.
• Replace a cuff that is worn, leaking or no longer closes firmly, as that changes the reading.

It is also reasonable to have your monitor checked against a clinic device. The American Heart Association’s guidance suggests having a health care provider check your monitor once a year, and bringing it to an appointment lets them compare its readings with their own equipment.