Health libraryBack to health library
How to use a peak flow meter
In 6 easy steps
How well are your lungs working?
Show me how
A peak flow meter can help measure how well your lungs are working and how well you're managing your asthma.
Set the meter at the bottom of the scale.
Stand up and make sure nothing is in your mouth. Take a deep breath.
Close your lips around the meter's mouthpiece.
Blow out as hard and fast as you can. Check the number where the marker landed.
Write down the number.
Repeat the process 2 more times. The highest number of the 3 numbers is your current peak flow.
What your numbers mean
"Good" or "bad" peak flow readings aren't the same for every person. Work with your doctor to find out what your zones of measurement should be as part of your asthma action plan. The zones often follow a traffic light system:
Danger. You're in the red zone if your reading is below 50 percent of your normal peak flow. This is a medical alert. Take your rescue medications. Call your doctor and follow your red-zone action plan.
Caution. You're in the yellow zone if your reading is 50 to 80 percent of your normal peak flow. This means your airways are narrowing. Follow your yellow-zone action plan.
You're good to go. You're in the green zone if your reading is 80 to 100 percent of your normal peak flow. This means your lungs are working fine. Continue following your asthma management plan.
Keep learning about asthma by following this link.
Sources: American Academy of Allergy, Asthma & Immunology; American Lung Association; National Institutes of Health
- American Academy of Allergy Asthma & Immunology. "Peak Flow Meter." https://www.aaaai.org/Tools-for-the-Public/Conditions-Library/Asthma/Peak-Flow-Meter.
- American Lung Association. "Measuring Your Peak Flow Rate." https://www.lung.org/lung-health-diseases/lung-disease-lookup/asthma/treatment/devices/peak-flow.
- MedlinePlus. "How to Use Your Peak Flow Meter." https://medlineplus.gov/ency/patientinstructions/000043.htm.