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How to Use a Peak Flow Meter

Peak flow meters measure how fast air is pushed out of the lungs. It can help to guide treatment for lung problems.

What You Will Need

  • Peak flow meter
  • Notebook to write down your measurements

Steps to Take

There are many types of meters. Read the instructions that came with your meter. General steps are:

  1. Stand up straight.
  2. Pick up the peak flow meter. Set the dial to zero.
  3. Slowly breathe out all the way. Then breathe in until your lungs are full.
  4. Peak_4.jpg Wrap your lips tightly around the mouthpiece. Keep your tongue away from the tube opening.
  5. Blow out as fast and hard as you can. The slide will move with your breath.
  6. Write down the number that you reached on the dial.
  7. Return the dial to zero and measure your breath again. Repeat steps 3 to 7. Do this two more times.
  8. Note the highest number that you reached. This is your peak flow. You will use this number to compare it to results in the future.

Wash the meter often. Let the mouthpiece and meter sit in warm soapy water for 2 to 3 minutes. Rinse well and let air dry. Wash after each use if you have a cold or flu. The meter will not work well if mucus or dirt have collected.

Common Questions

Q. I get very different numbers each time I blow into the peak flow meter. Does this mean that my asthma is out of control?

A. It is normal to have a little change in numbers. Large changes may mean you are not using your meter the right way. Reread your meter's instructions. Try the meter again. Talk to your care team if the problem continues.

Q. My last peak flow reading is lower than usual, but I feel fine. Should I be worried?

A. You may want to try a second round of tests with the meter. However, peak flow can be lowered hours or even days before people with asthma have an attack. Asthma action plans should be followed.

Q. How often should I use my peak flow meter?

A. Follow your care plan. Most people will use the meter at least once a day. It should also be used when symptoms happen or change.

Call Your Doctor

Call your doctor if your:

  • Reading is less than 80% of your usual peak flow and treatment has not improved it
  • Peak flow changes a lot from day to day or from morning to night
  • Flow is less than 50% of your usual peak flow reading, which may be a sign of an emergency

American Lung Association

Family Doctor—The American Academy of Family Physicians


Asthma Society of Canada

The College of Family Physicians of Canada


Add peak expiratory flow: measuring. EBSCO Nursing Reference Center website. Available at: https://www.ebscohost.com/nursing/products/nursing-reference-center. Accessed December 8, 2020.

Asthma. Family Doctor—American Academy of Family Physicians website. Available at: http://familydoctor.org/familydoctor/en/diseases-conditions/asthma/diagnosis-tests.html. Accessed December 8, 2020.

Measuring your peak flow rate. American Lung Association website. Available at: https://www.lung.org/lung-health-and-diseases/lung-disease-lookup/asthma/living-with-asthma/managing-asthma/measuring-your-peak-flow-rate.html. Accessed December 8, 2020.

Last reviewed September 2020 by EBSCO Medical Review Board Chelsea Skucek, MSN, BS, RNC-NIC  Last Updated: 6/2/2021