Peak Flow Meter: Uses, Procedure, Results

An important tool for effective asthma monitoring and more

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A peak flow meter is a portable device that measures your peak expiratory flow rate (PEFR)—that is, how quickly your lungs expel air during a forceful exhalation after you fully inhale. Regularly conducting a peak flow test at home and tracking the results can help you monitor your breathing status and respiratory disease.

In particular, knowing your normal peak flow rate—and detecting when you are not achieving it—can be an important part of your asthma treatment and asthma action plan.

Peak flow monitoring is most often used in asthma management but is also helpful for managing emphysema and chronic bronchitis.

how to take a peak flow measurement

Verywell / Cindy Chung

Purpose of Test

Monitoring peak flow is an essential component of managing asthma, as it allows you to keep tabs on how open your airways (bronchi) are. When your PEFR begins to decrease, it's a sign your airways are starting to narrow and your asthma is getting worse.

Regular use of a peak flow meter can:

  • Help you keep track of how well you're breathing on a regular basis
  • Indicate an impending asthma attack or worsening of your asthma symptoms
  • Help you know when it is time to activate your asthma action plan
  • Help you identify asthma symptom triggers
  • Determine whether your management plan is effective or if your symptoms are getting worse and your treatment needs to be adjusted

Peak flow monitoring also can be useful to people with emphysema or chronic bronchitis to track breathing changes and determine if treatment plans, including medications, are working.

Peak flow monitoring usually is recommended for adults and children who are at least 5 and have moderate to severe asthma, or for those whose symptoms aren't under control and whose medication is being adjusted. It can be particularly helpful for people who have mild asthma and aren't on daily medication.

Depending on the severity of your asthma, your healthcare provider may want you to check your peak flow several times a day, once a day, every few days, or just at certain times. The most common recommendation is once a day in the morning before taking your asthma medication.

Because asthma may worsen gradually, your peak flow measurement may start to decrease hours—and sometimes even days—before you notice any symptoms.

If your child has been diagnosed with asthma and is younger than 5, they likely will not be able to manage using a peak flow meter. However, some younger children are able to do it. Even if not, it doesn't hurt to have them practice getting used to how it works so they are prepared when they are older.


The risks of peak flow measurement are minimal but can include coughing or feeling lightheaded from filling your lungs with air before you blow into the device.

If you begin to feel strange, take a deep breath and allow your body and mind to calm down. Do mention the experience to your healthcare provider, as it may indicate poor control of your asthma. However, if for some reason you continue to feel "off," uncomfortable, or anxious after a peak flow test, seek urgent medical attention.

While it's not a direct health risk of the test itself, parents should know that peak flow readings for children are sometimes less reliable than for adults. Measurements can be falsely increased with tongue movements or spitting and decreased with not enough effort in the breath, so it's important to also pay close attention to your child's symptoms—not just their peak flow results.

Before the Test

There is little to do to prepare for peak flow testing, but you will likely need to obtain your peak flow meter on your own and be ready to record the information it provides.

Your healthcare provider will probably have you find your personal best peak flow number to figure out what's normal for you before you start taking routine readings. Make sure you are clear about what that involves before beginning.

Choose a Peak Flow Meter

You'll do your peak flow measurements at home, school, or work, depending on when and how often your healthcare provider wants you to do them. The meter is a handheld device that does not need to be plugged in, which allows you to test yourself virtually anywhere.

You can buy your peak flow meter over the counter at a pharmacy, medical supply store, or online. Always use the same brand and model peak flow meter every time to avoid meter-to-meter variations. (If you plan to test at work and at home, for example, consider buying two of the exact same devices.) Your healthcare provider can make recommendations.

Peak flow meters are relatively inexpensive, especially plastic devices that have a spring system. These are typically $10 to $25.

Digital peak flow meters are pricier—anywhere from $30 to $100. Certain digital models can record and track measurements electronically, which may be a feature worth considering.

Preliminary research suggests using a digital monitoring device along with a linked smartphone app that records the measurements may help improve the consistency of PEFR monitoring and the reliability of data compared to a standard device and manual log.

Contact your insurance company to discuss what type of peak flow meter they'll cover, as well as what you may need to pay in terms of a co-payment or co-insurance.

Determine Your Personal Best

Your personal best peak flow is the highest peak flow measurement you obtain over a period of two to three weeks when your condition is effectively controlled, meaning that you feel well and aren't experiencing respiratory symptoms. Testing is typically done two to four times a day at the same times every day.

Although there are "normal" peak flow rates based on a person's height, age, sex, and race, these are averages for large groups of people—many of whom don't have lung diseases. Your normal may be very different than the normal on a generic reference chart, which is why it's important to establish your personal best peak flow. This measurement is the one against which all your other peak flow measurements will be compared moving forward.

You will receive instructions from your healthcare provider or asthma educator regarding how to go about determining your personal best and what your next steps should be. Ask any questions you have before taking your first measurement.

In particular, be sure you are clear about:

  • Frequency and duration of personal best testing: How many times a day? At what times? For how many weeks?
  • Follow-up: Do you need to make an appointment to discuss peak flow zones and your action plan once you've determined your personal best, or can that be done over the phone?
  • Future testing: How often and at what time of day should you measure your peak flow once your personal best and peak flow zones are established? Should you measure your peak flow before or after you have taken your asthma medication?
  • Testing adjustments: What circumstances might warrant extra measurements (e.g., sickness, worsening symptoms, an asthma attack, or changing medications)?

Keep a Record

With time, peak flow testing can become a matter of routine. But the information you gather from each one is valuable, so it's important to keep a manual log of your measurements if they are not automatically being tracked digitally. Consider purchasing a pocket-size notebook that you can dedicate to this or download and use a smartphone app designed for this purpose.

You may also want to seriously consider keeping a daily record of your asthma, chronic bronchitis, or emphysema symptoms. Log the medications and doses you're taking, and any factors you've been exposed to that you think might trigger your symptoms, such as smoke, certain foods, cold, exercise, or high pollen count.

All of this information together can give you and your healthcare provider a more complete picture of how your treatment plan is working and help you see patterns.

During the Test

How you use a peak flow meter is the same regardless of whether you are finding your personal best reading or doing routine measurements, though the recommended testing schedule may differ.

A peak flow test normally takes a minute or two. Readings are most accurate if they are taken at the same time every day. When taken in the morning, it's usually best to do so before taking asthma medication. Follow your healthcare provider's instructions regarding when to perform your peak flow tests.


Check the peak flow meter for obstructions or foreign objects, and make sure it is clean and dry before you use it. Not only can a dirty peak flow meter affect the accuracy of your readings, but it can also potentially make you sick.

Follow the care instructions that come with the device. For the plastic, spring system type, general instructions are to let it soak in a bowl of warm water and mild dish soap for three to five minutes, swish it around, rinse it out, and let it dry completely before use.

There are no food or drink restrictions for checking your peak flow. Remove anything you might have in your mouth, such as gum or candy, before you blow into the device.

Throughout the Test

Follow these steps to conduct a peak flow test:

  1. If you're using a meter with a spring system (not digital), make sure the marker on your meter is at 0 or the lowest number. If you're using a digital meter, turn it on.
  2. Attach the mouthpiece if it's not already connected.
  3. Stand up, if possible. If not, sit up straight.
  4. Inhale deeply, filling up your lungs as much as you can.
  5. While holding your breath, put the meter's mouthpiece in your mouth, making sure that your tongue is underneath the mouthpiece and your lips are closed tightly to create a seal around it.
  6. Blow air out as hard and as fast as you can in one breath for no more than one second.
  7. If you coughed, your tongue got in the way, or you didn't get a good seal, repeat these steps and discard that reading. If not, write down the number on the meter at which the marker now rests (spring system) or that shows on your the screen (digital), if not logged electronically.
  8. Repeat steps 1 to 7 two more times as soon as you can after you've taken a few normal breaths. The numbers should all be very close together if you're doing it right each time. If they're not, try again until you get three numbers that are similar.

If you aren't sure you're using your peak flow meter correctly, check back with your healthcare provider or your pharmacist to have them assess your technique and help you correct any mistakes you might be making.

After the Test

When you're finished taking these readings, record the highest of the three numbers in your peak flow diary or chart. Don't average the numbers together, use the highest one.

You can then go about your normal activities as usual.

Otherwise, clean your peak flow meter according to the manufacturer's instructions, or at least once a week. If you're sick with a cold or the flu, wash the device and/or the mouthpiece (depending on whether you're using a digital or plastic one) after each use.

Interpreting Results

If you're just starting out and establishing your personal best peak flow, your healthcare provider will review your readings and determine your peak flow zones. These ranges are color-coded like a stoplight to indicate levels of concern:

  • Green zone: Your asthma is well-controlled.
  • Yellow zone: Your asthma is starting to get worse and needs attention.
  • Red zone: Your condition has become a potential emergency.

Your healthcare provider will work with you to set up an action plan that tells you exactly what to do if your numbers dip into the yellow or red zones.

If you are at the point at which you are routinely monitoring your peak flow, you will be able to reference your results and your asthma action plan to determine whether your rate is satisfactory (green) or has dropped into the warning (yellow) or danger (red) zones.

Peak Flow Zones  % of Personal Best Meaning
Green 80% to 100% •Condition is stable and well-controlled
•Likely no symptoms
•Keep taking medications as prescribed
Yellow 50% to 80% •Airway is beginning to narrow, though you may not have symptoms yet
•Use rescue inhaler or have medication adjusted if symptoms are occurring (per your action plan)
Red Under 50% •Possible medical emergency
•Airway has significantly narrowed; may be fatal without treatment
•Follow your action plan (rescue inhaler, medication)
•Call for help; never drive yourself to the ER


Lung conditions, including asthma, have the potential to change, so you should see your healthcare provider regularly—even when you're doing well. Your medications may need some tweaking here and there, depending on your symptoms. If your asthma has been well controlled for a long time, you may even be able to decrease the dose of your medication with careful monitoring.

Whenever your peak flow numbers start to fall into the yellow or red zones, you may also need to see your healthcare provider to discuss changes to your treatment plan. However, this will depend on what your action plan says, as well as how long you're in a particular zone.

A personal best peak flow should be remeasured every year or whenever your healthcare provider recommends, since your condition can change. For kids, this takes into consideration growth and expanding lung capacity.

If you start using a new peak flow meter, you will also need to remeasure your personal best, since readings can vary from brand to brand and even meter to meter.

A Word From Verywell

Since self-monitoring is such an important part of a successful asthma care plan, using a peak flow meter to measure your peak flow can significantly improve the effectiveness of your treatment. As you learn what your asthma triggers are, monitor your peak flow for gradual changes that you may not otherwise notice, and track the effects of all of your medications, you will also learn more about your asthma, how to manage it well, and what triggers to avoid.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. National Heart, Lung, and Blood Institute. Expert panel report 3 (EPR3): Guidelines for the diagnosis and management of asthma.

  3. Asthma and Allergy Foundation of America. Peak flow meters.

  4. American Academy of Pediatrics. Peak flow meter.

  5. University of Rochester Medical Center. Peak flow meter.

  6. Antalffy T, De Simoni A, Griffiths CJ. Promising peak flow diary compliance with an electronic peak flow meter and linked smartphone app. NPJ Prim Care Respir Med. 2020;30(1):19. doi:10.1038/s41533-020-0178-y

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By Pat Bass, MD
Dr. Bass is a board-certified internist, pediatrician, and a Fellow of the American Academy of Pediatrics and the American College of Physicians.