Peak Flow Meter

A peak flow meter measures how fast air comes out of your lungs when you exhale forcefully. Readings from the meter can help you or your child recognize early signs of worsening asthma. Keeping track of peak flow numbers is part of your Asthma Action Plan.

What is a peak flow meter and why use one?

A peak flow meter measures how fast you can push air out of your lungs when you blow out as hard and as fast as you can. This is called peak flow.

Your peak flows measure how open the airways are in the lungs. Your peak flow may drop early even before you feel bad. This drop tells you that your asthma may be getting worse. Measuring your peak flow may help you learn what caused or “triggered” the drop, helps decide which medicines to add or take away and when you may need emergency care.


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How do you use the peak flow meter?

A peak flow meter is simple to use. To measure your peak flow:

  1. Sit or stand up straight. Whichever you choose, make sure you do it this way each time.
  2. Make sure the red marker is at the bottom of the meter.
  3. Take a deep breath, filling your lungs completely.
  4. Place the mouthpiece in your mouth. Close your lips tightly on the peak flow meter’s mouthpiece.
  5. Blast the air out as hard and as fast as possible in a single blow.
  6. Write down the number by the red marker on the meter.
  7. Put the red marker back at the bottom of the peak flow meter and repeat these steps three times.
  8. The highest of these three readings is your daily peak flow.
  9. Write down the highest of the three readings on a sheet of paper, calendar or in your asthma diary.
  10. Record any symptoms you are having, like wheezing, chest tightness, shortness of breath or coughing and if you’ve taken your rescue/emergency medication.

How do you find your "personal best" peak flow?

The "personal or usual best" peak flow is the highest number you can perform over a two-week period when asthma is under good control. Good control means you feel good and do not have any symptoms. You’ll compare all of your other peak flow readings to your personal best peak flow number.

To find your personal best peak flow:

  • Perform peak flow testing twice a day for two weeks.
  • Do them at the same time in the morning and in the early evening.
  • Do the test before taking any inhalers, or as instructed by your healthcare provider.

Once you have determined your personal best peak flow number, continue to perform peak flows daily or as instructed by your healthcare provider. Regular use of peak flow will help you recognize early decreases in airflow and will be used to guide your asthma care. Your caregiver may use these numbers to create a plan for helping you control your asthma. This is called an Asthma Action Plan.


How do you use your Asthma Action Plan?

Keeping a daily record of your peak flows and understanding how this relates to changes in asthma will help you to better manage asthma episodes. To help with understanding how this works, caregivers use the “traffic light” system.

Your Asthma Action Plan has three zones: green, yellow and red.

  • Green zone: Your asthma is well-controlled. Peak flow is 80% to 100% of your personal best.
  • Yellow zone: Your asthma is getting worse or is poorly controlled. Peak flow is 50% to 80% of your personal best.
  • Red zone: Your asthma is severe. It requires emergency care. Peak flow is less than 50% of your personal best.

To find the number ranges for your Asthma Action Plan zones, multiply your personal best peak flow by 1.0 (100%), 0.8 (80%), and 0.5 (50%). Record these ranges in your asthma diary so that you can refer to them easily.

For example, if your personal best peak flow is 400 LPM, the zones will be:

  • Green zone: 320 LPM to 400 LPM (80% to 100%).
  • Yellow zone: 200 LPM to 320 LPM (50% to 80%).
  • Red zone: Less than 200 LPM (less than 50%).

If you are in the yellow or red zone, you will need to adjust your medicine according to your healthcare provider’s instructions. You’ll use the peak flow values and symptoms to take action to get or stay healthy. Make sure you understand and can follow your Asthma Action Plan. If you have any questions, ask your healthcare provider for an explanation.

When you see your healthcare provider, bring the information you’ve recorded in your asthma diary along with your peak flow meter to make sure you’re using it correctly.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 12/15/2020.

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