Measuring Blood Pressure
Choose the right cuff, take an accurate manual or automatic reading, avoid common errors and know which readings to report.
Table of contents
Blood pressure is the force of blood pushing against artery walls. It is written as two numbers, such as 118/76, in millimeters of mercury (mmHg). The top number, systolic, is the pressure when the heart contracts and pumps blood. The bottom number, diastolic, is the pressure when the heart relaxes between beats. A reading guides real decisions about medicine and care, so a small technique error can matter a lot.
What You Will Be Able to Do
- Prepare the person so the reading is accurate.
- Choose and place the correct cuff.
- Take a manual reading with a stethoscope.
- Use an automatic machine correctly.
- Know the adult categories and which readings to report.
Prepare the Person
For a resting reading, the person should:
- Avoid caffeine, exercise and smoking for 30 minutes first, when you can plan ahead.
- Empty their bladder.
- Sit quietly for at least 5 minutes with their back supported and feet flat on the floor, legs uncrossed.
- Rest the arm on a table or pillow so the cuff is at heart level.
- Not talk during the reading.
If the person cannot sit, record the position they were in, such as lying down. Use the same arm each time unless the care plan says otherwise. Do not use an arm with a dialysis fistula, an IV, a recent mastectomy on that side or any other limb marked as restricted. Check the care plan first.
Choosing the Cuff
Cuff size is the error people make most often.
| Cuff | Effect on the reading |
|---|---|
| Too small | Falsely high |
| Too large | Falsely low |
| Correct | Bladder wraps about 80 percent of the way around the upper arm |
Use the range marks printed on the cuff. If the arm falls outside them, go up or down a size. Place the cuff on bare skin, not over a sleeve, with the lower edge about 1 inch above the bend of the elbow. Line up the artery marker with the brachial artery, on the inner side of the arm.
Taking a Manual Reading
You need a cuff with a gauge and a stethoscope. Wipe the earpieces and diaphragm first, and clean your hands.
- Find the radial pulse at the wrist. Inflate the cuff until you can no longer feel it, and note that number. Deflate the cuff fully and wait about a minute.
- Put the stethoscope earpieces in, pointing forward.
- Find the brachial pulse at the inner bend of the elbow, and place the diaphragm over it, below the cuff. Do not tuck it under the cuff.
- Close the valve and inflate quickly to about 30 mmHg above the number from step 1.
- Open the valve slowly so the needle falls about 2 to 3 mmHg per second.
- Note the first clear tapping sound. These sounds are called Korotkoff sounds, and the first one is the systolic reading.
- Keep listening. The point where the sounds disappear is the diastolic reading.
- Let the rest of the air out and remove the cuff.
- Record the reading, the arm and the position. For example: "132/84, left arm, sitting."
If you need to repeat the reading, wait 1 to 2 minutes so the arm can recover. If you did not hear the numbers clearly, do it again. Do not guess or round to the nearest ten. Use even numbers on a gauge marked in 2 mmHg steps.
Using an Automatic Machine
Automatic monitors are common in hospitals, clinics and homes.
- Prepare the person in the same way, and use the correct cuff.
- Keep the arm still and the person silent during the measurement.
- Press start and wait.
- Record the reading.
Machines can give wrong numbers when a person has an irregular heartbeat, is shivering or moves during the reading. If a number looks wrong, or does not match how the person looks, recheck it manually or ask the nurse. Check the device was calibrated as your employer requires.
Adult Blood Pressure Categories
These categories come from the 2025 American Heart Association and American College of Cardiology guideline. They are for adults and they are used to diagnose over time, not from one reading.
| Category | Systolic | Diastolic |
|---|---|---|
| Normal | Under 120 | and under 80 |
| Elevated | 120 to 129 | and under 80 |
| Stage 1 hypertension | 130 to 139 | or 80 to 89 |
| Stage 2 hypertension | 140 or higher | or 90 or higher |
| Severe hypertension | Over 180 | or over 120 |
Note the word "or." If either number falls in a higher category, the higher category applies. A reading of 140/88 is Stage 2, for example, because the systolic is 140. A reading of 128/92 is also Stage 2, because the diastolic is 92.
The top row is often called a hypertensive crisis. The American Heart Association now separates it into two situations:
- Over 180 or over 120 with no symptoms: wait a minute and take it again. If it is still that high, this is severe hypertension. Tell the nurse right away.
- Over 180 or over 120 with symptoms such as chest pain, shortness of breath, back pain, numbness, weakness, vision changes or trouble speaking: this is an emergency. Call 911.
Warning: Do not wait for a second reading if the person has those symptoms. Call 911 first.
Low Readings
There is no single cutoff for low blood pressure. Many people live safely with a reading in the 90s. What matters is the change from their usual reading and how they feel. Report a systolic under 90, or a reading well below their baseline, right away. An example would be someone who usually runs 130/80 and now reads 88/56, especially if they are dizzy or confused. Follow the care plan limits.
Common Mistakes
| Mistake | What it causes |
|---|---|
| Arm hanging at the side, below the heart | Falsely high |
| Measuring over a sleeve | Inaccurate reading |
| Legs crossed, back unsupported or person talking | Falsely high |
| No rest period | Falsely high |
| Deflating too fast | Missed sounds and a wrong number |
| Stopping at the first odd number | The person may get the wrong treatment |
Check Your Understanding
1. A reading is 165/100 on a patient who just rushed back from the bathroom. What should you do?
Have the patient sit and rest for 5 minutes, then repeat it with the correct technique. Report the reading if it stays high.
2. A patient with a very large arm is using a standard cuff. How would that affect the reading?
The cuff is too small, so the reading will be falsely high. Get a larger cuff.
3. A patient's reading is 186/118. She feels fine. What do you do?
Wait a minute and repeat it. If it is still over 180, tell the nurse right away. If she develops symptoms such as chest pain or trouble speaking, call 911.
4. You hear the first tapping sound at 142 and the sound disappears at 86. What do you record, and what category is it?
Record 142/86 with the arm and position. It falls in Stage 2 because the systolic is 140 or higher, and you report it according to the care plan.
Key Takeaways
- The top number is pressure during a heartbeat, and the bottom number is pressure between beats.
- Rest 5 minutes, support the back, feet and arm, and do not talk.
- A cuff too small reads high, and a cuff too large reads low.
- The first sound is systolic, and the last sound is diastolic.
- 140/90 or higher is Stage 2.
- Over 180 or over 120 is severe, and with symptoms, call 911.