Way to Grow Header

Peak Flow Meters (PFM)

(757) 668-7000

A Peak Flow Meter (PFM) is a device used to measure the fastest speed in which you can blow air out of your lungs. During an asthma flare up, the large airways in your lungs slowly begin to narrow. This will slow the speed of air leaving your lungs and can be measured by a PFM. This measurement is very important to you and your doctor in judging how well or how poor your asthma is being controlled.

Why should a peak flow meter be used:

Using a PFM correctly removes a lot of guesswork out of managing your asthma. It can provide you, your parents, your doctor, or even your school teachers with information about how open the airways are in your lungs. It is important to do this correctly.

The PFM can detect small changes in your large airways before you even start to wheeze. Using a PFM every day will let you know when your peak flows are starting to drop. This allows you to make early changes in your medicine or routine to help prevent your asthma symptoms from getting worse. The PFM can also identify the value at which you will need to call your doctor or go to the Emergency Room.

How to use a peak flow meter:

  1. Use the PFM once daily and whenever you are experiencing early warning signs. Always use the PFM before you take your reliever medicine.
  2. Hold the PFM by the handle.
  3. Before each use, make sure the pointer is reset to zero.
  4. Stand up straight. Remove chewing gum or any food from your mouth.
  5. Take a deep breath and put the mouthpiece in your mouth. Seal your lips and teeth tightly around the mouthpiece.
  6. Blow out as hard and as fast as you can. Remember a "fast blast" is better than a "slow blow".
  7. Note the number where the pointer has stopped on the scale.
  8. Reset the pointer to zero.
  9. Repeat this routine three times. You will know you have done the technique correctly when the numbers from all three tries are close together.
  10. Record the highest of the three readings on a graph or in a notebook. Do not average these numbers together. This is called your "peak flow".
  11. Use your peak flow meter 1 time per day. Measure your peak flows about the same time each day. One way might be when you first wake-up or at bedtime. It is helpful to write your peak flow on a calendar.

Peak Flow Zones:

Three zones are used to explain your peak flow readings - green zone, yellow zone, and red zone. These zones are different for each person. Your doctor or nurse will help you figure out your zones and tell you what your highest peak flow should be.

Your peak flow zones are like the three lights on a traffic signal - green, yellow, and red.

Green Zone:

This is the GO zone! This zone is from 80-100% of your highest peak flow reading. This is the zone you should be in every day. This is a signal that air moves well through your large airways and that you can do your usual activities and go to sleep without trouble. When your peak flow readings are in this zone, you should:

  • Avoid asthma triggers
  • Use your controller medicines every day.
  • Use the reliever medicine 15-20 minutes before exercise if you have exercise induced asthma.

Yellow Zone:

This is the CAUTION or SLOW DOWN zone! This zone is from 50-80% of your highest peak flow reading. This is a clue that your large airways are starting to narrow. You may begin to have mild symptoms. You may be coughing, feel tired, feel short of breath, or feel like your chest is tight. These symptoms may keep you from your usual activities or from sleeping well. To keep your peak flow numbers from getting worse and get your asthma back under control, you will need to:

  • Continue to use your controller medicine as your doctor has ordered and avoid asthma triggers.
  • Use your reliever medicine as ordered by your doctor.
  • Make sure you are using the proper technique with your metered-dose inhaler and spacer.

Red Zone:

This is the STOP zone! This zone is less than 50% of your highest peak flow reading. Readings in this zone are a medical emergency and you will need to get help right away. This means severe narrowing of your large airways has occurred. You may now be coughing, very short of breath, wheezing both when breathing in and out, or having retractions. You may also have problems walking and talking. Take your reliever medicine now and call your doctor.

When to call your child's doctor:

  • Peak flows are in the yellow zone greater than 24 hours.
  • Peak flows are in the red zone.
  • Reliever medicine is needed more often than every 4 hours.
  • Reliever medicine does not help your child.


  • your child has trouble talking due to shortness of breath
  • your child’s lips or fingernails are gray or blue
  • your child seems confused or cannot answer you. 

Disclaimer: This information is not intended to substitute or replace the professional medical advice you receive from your child's physician. The content provided on this page is for informational purposes only, and was not designed to diagnose or treat a health problem or disease. Please consult your child's physician with any questions or concerns you may have regarding a medical condition.

Reviewed: 03/05

(757) 668-7000