How to take and read blood pressure at home.
Getting a number you can trust comes first. Here are the seven steps to a good reading, then what the two numbers mean once you have one.
How to take a blood pressure reading at home.
The same arm on the same day can give two very different numbers depending on how the reading was taken. These seven steps are what separate a number worth writing down from one that just worries you.
- 1
Skip caffeine, tobacco and exercise for 30 minutes
All three raise blood pressure for a while. A reading taken straight after any of them tells you about the coffee, not about you.
- 2
Empty your bladder
A full bladder can add several points to a reading. It is the easiest error on this list to remove.
- 3
Sit still for 5 minutes
Sit in a chair with your back supported and both feet flat on the floor. Do not cross your legs. Do not talk, and do not scroll your phone. Just sit.
- 4
Put the cuff on a bare upper arm
Take your arm out of the sleeve rather than rolling it up, because a bunched sleeve squeezes the arm. The bottom edge of the cuff sits about an inch above the bend of your elbow.
- 5
Rest your arm at heart level
Support your arm on a table so the cuff is level with your heart. An arm hanging by your side reads high. An arm held up reads low.
- 6
Take two readings, one minute apart
Write both down. If they differ by more than about 5 points, take a third. Averaging is what makes the number stable.
- 7
Measure at the same times each day
Morning before medication, and evening. What a doctor can use is a run of readings taken the same way, not one number from one moment.
The two numbers.
Systolic pressure
The top number. It measures the pressure in your arteries when your heart beats and pushes blood out. This is always the higher number.
Diastolic pressure
The bottom number. It measures the pressure in your arteries between beats, when your heart is resting and refilling with blood.
How it is written: Blood pressure is written as systolic over diastolic. A reading of 120/80 means systolic 120, diastolic 80. Both numbers are measured in millimeters of mercury (mmHg).
The five AHA categories.
The American Heart Association puts every reading into one of five categories. Here they are in plain English.
Under 120 / Under 80 mmHg
Your blood pressure is healthy. Keep doing what you are doing.
120 to 129 / Under 80 mmHg
Higher than ideal. Lifestyle changes can bring it back to normal without medication.
130 to 139 / 80 to 89 mmHg
Hypertension. Talk to your doctor. Lifestyle changes and possibly medication.
140 or higher / 90 or higher mmHg
High blood pressure that usually needs medication along with lifestyle changes.
Over 180 / Over 120 mmHg
Wait a minute and take it again. If it is still that high, call 911 if you also have symptoms, or contact your doctor right away if you do not.
Source: American Heart Association 2025 guidelines. Consult your doctor for personal medical advice.
Which number decides your category?
Look at both numbers. Whichever falls in the higher category is your classification.
Example: A reading of 132/78 has a systolic in Stage 1 (130 to 139) and a diastolic in Normal (under 80). The classification is Stage 1 Hypertension because the systolic is higher.
Either number alone can push you into a higher category. This is why you cannot ignore the diastolic even if the systolic looks fine.
Common errors that skew your reading.
Most people take their blood pressure incorrectly. These five mistakes are the most common ones, and each can add 5 to 15 mmHg to your number.
Sit upright with back supported, feet flat on the floor, and arm resting at heart level on a table. A slouched or awkward position can add 5 to 10 mmHg to your reading.
Avoid caffeine, tobacco, and vigorous exercise for at least 30 minutes before measuring. Both raise blood pressure temporarily and will skew your reading.
An undersized cuff reads high. An oversized cuff reads low. Most monitors ship with one wide range cuff that fits 8.6 to 16.5 in (22 to 42 cm), and if your arm falls outside that you need a different cuff, not a different monitor. Measure your arm before you trust any reading.
Sit quietly for 5 minutes before measuring. Walking in and immediately taking your reading adds stress-related elevation to the number.
Take two readings at least a minute apart and average them. If they differ by more than 5 mmHg, take a third and average all three. Single readings have more error.
When to call a doctor.
Home monitoring is valuable but it is not a replacement for medical care. Contact a doctor or call 911 if any of these apply.
- Your reading is over 180 or over 120. Wait a minute and take it again. If it is still that high and you have chest pain, shortness of breath, back pain, numbness, weakness, a change in vision or trouble speaking, call 911. If you do not have those symptoms, contact your doctor right away.
- You have a consistent reading of 140/90 or higher over several days.
- Your blood pressure is dropping suddenly and you feel dizzy or faint.
- Your readings are suddenly much higher or lower than usual with no clear reason.
- You have symptoms like chest pain, shortness of breath, or vision changes alongside high readings.
Start tracking your numbers.
BP Central logs every reading, shows the range it falls in, and builds a trend you can share with your doctor.
Now keep the readings somewhere useful. A reading you took properly and then lost is the same as one you never took.
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First 10 readings free. Then $6.99 once. No subscription. iPhone.
Why you got two different numbers five minutes apart
Because that is what blood pressure does. It is not a fixed property like your height. It is a moving quantity that responds to the last few minutes of your life, and a monitor that gave you an identical number twice would be the suspicious one.
It falls while you sleep and climbs before you wake. It rises when you stand up, when you talk, when you are cold, when your bladder is full, and for a while after coffee or a cigarette. None of that is a fault in the device and none of it is a symptom.
This is exactly why the guidance asks for 2 readings at a sitting and 28 across a week, rather than one and a verdict. You are not trying to catch the true number. You are trying to see the middle of the cloud.
When to take another reading
- Always, once, a minute after the first. Two readings a sitting is the routine, not a reaction to a number you dislike. Take both every time and write both down.
- If something obviously interfered. You talked, the cuff slipped, your arm was hanging, a dog barked. Note it, wait, and take it again properly.
- If the cuff felt wrong on your arm. Loose, twisted, over a sleeve, or so tight it hurt. That reading is not worth keeping.
What not to do is measure repeatedly until you get a number you like. Taking six readings and recording the lowest does not give you a lower blood pressure. It gives you a log that is wrong in a direction you chose, and a clinician working from it is working from fiction.
How much technique actually changes the number
More than most people assume, and the largest single factor is not posture. It is whether the cuff is the right size for your arm.
In a randomised trial, using a regular cuff on people who needed an extra-large one overstated systolic by +19.5 mmHg. For people who needed a large cuff it was +4.8 mmHg.
Ishigami J, Charleston J, Miller ER III, et al. Effects of Cuff Size on the Accuracy of Blood Pressure Readings: The Cuff(SZ) Randomized Crossover Trial. JAMA Internal Medicine, 2023.
That is larger than the width of a whole category. Before you take any reading seriously, it is worth knowing the cuff fits — which takes a tape measure and one minute.
You got one high reading. Now what?
First, do not diagnose yourself from it. One reading is one sample, and the categories are written about readings that are consistently in a range.
Sit quietly for five minutes and take it again, properly. If the second reading is much lower, the first one probably caught you mid-something. Write both down anyway — the log is a record of what happened, not a record of what you wanted to happen.
When it is not a wait-and-see
If a reading is very high and you also have chest pain, shortness of breath, back pain, numbness or weakness, a change in vision, or trouble speaking, call 911. That combination is not a measurement question and it is not something to re-check in five minutes.
Short of that, the useful response to a surprising number is not a single better reading. It is a set of them, taken properly, averaged, and taken to somebody who can examine you.