Updated 12 July 2016

Peak flow meter

Asthma is a chronic, inflammatory lung disease that may or may not be triggered by allergens. Learn more about the peak flow meter.



When you have asthma, the air passages within the lungs are constantly swollen, restricting the amount of air allowed to pass through the trachea. Asthmatics have recurrent breathing problems and a tendency to cough and wheeze.

While there is currently no cure for asthma, proper treatment and management can help alleviate symptoms.

A peak flow meter helps patients monitor their asthma and prepare for asthmatic exacerbations. This portable device measures how well the lungs are able to expel air.


Dr. B.M. Wright created the first meter specifically designed to measure the airflow of the lungs in the late 1950s. Today, the device has evolved to a more portable and cost-affordable version. Currently, there are several different types of peak flow meters, which are available over-the-counter. Individuals should consult their healthcare providers to determine which is best for them.


A peak flow meter is made of a plastic tube with a mouthpiece on the end. A scale is located inside the device to measure the force of air that is expelled from the lungs and blown through the tube. This force, measured in liters per minute, is known as the peak expiratory flow (PEF).


Peak flow meters are most helpful for asthmatics who take asthma medication daily. Children as young as three years old have been able to use a peak flow meter safely and effectively.

There are several types of peak flow meters, which are available over-the-counter. A low-range peak flow meter is used for small children, and a standard-range meter is used for older children, teenagers and adults. A physician or pharmacist can help patients determine which type to use. Examples of peak flow meters include: ASSESS©, AsthmaCheck©, POCKETPEAK© and MicroPeak©.


To use the device, first slide the pointer all the way down to the bottom of the scale. Then stand up, remove any gum or food from the mouth, and take a deep breath. Place the lips over the mouthpiece, making sure there are no gaps for air to escape. Do not put the tongue inside the hole. Blow as quickly and as forcefully as possible into the tube. Do not breathe out slowly or for a long period of time because the device is designed to measure how fast and hard the individual can expel air out of the lungs.

Once the air is expelled, take the meter of the mouth, and note the number next to the pointer. If the individual coughs or makes a mistake, the number is not considered an accurate reading. Repeat the procedure twice more, and then record the highest of the three readings. Do not calculate the average. It is recommended that individuals keep a chart, including the date and time of each peak flow reading.


Individuals should determine their personal best peak flow reading. This is the highest number the individual can achieve when the asthma is under good control. Good control means that the patient feels healthy and is not experiencing asthma symptoms.

Take peak expiratory flow (PEF) readings at least twice a day for two to three weeks. It is recommended that individuals measure their peak flow in the morning and evening, after taking short-acting inhalers, when asthma symptoms occur and any other time the physician suggests. Record the readings when PEF is measured.

After two or three weeks, look at the recorded numbers and find the highest reading. This number is considered the personal best peak flow reading. Personal best readings vary among individuals, even if they are the same age, weight and height.

Three numbers are calculated from the personal best reading, and they are used to establish three separate "zones." These zones are based on percentages of the personal best reading and are merely guidelines.

Green zone: The green zone is more than 80% of the personal best reading. Readings in this zone signal that the asthma is under good control. Medications should be taken as usual.

Yellow zone: The yellow zone is 50-80% of the personal best reading. This zone indicates caution because there is some airway narrowing. Individuals are recommended to take a short-acting, quick-relief medication right away to prevent asthma symptoms. Individuals should also consult their healthcare providers to determine whether daily medicines should be altered.

Red zone: The red zone is less than 50% of the personal best reading. This signals a medical alert because there is significant narrowing of the airway passages. Individuals should take their quick-relief medication immediately (e.g., oral steroids), and call their physicians or go to the emergency department at the hospital to determine the best course of action.

If an individual's peak flow reading increases 20% or more after taking a short-acting inhaled quick-relief medicine, a qualified healthcare provider should be consulted to determine whether another medication or higher doses would help control the asthma symptoms.


The muscles in the upper airways contract during an asthma attack, making it difficult for the lungs to take in and release air. However, this narrowing of the airways does not happen suddenly. In fact, the airway may start to narrow hours before the first symptoms of asthma arise.

The peak flow meter can help a patient determine when the airway begins to narrow, possibly before symptoms occur. A 20-30% decrease in an individual's PEF might indicate that asthma mediation is necessary to prevent an asthma attack. Taking medications before symptoms appear may help prevent severe exacerbations.

In addition, a peak flow meter can help patients and physicians learn what makes triggers the asthma (makes the asthma worse), decide whether the current treatment plan is working, decide when to add or stop medication(s), and decide whether emergency care is necessary.


This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (

  • American Academy of Allergy Asthma and Immunology. Accessed March 22, 2007.
  • American Lung Association. Peak Flow Meter. Accessed March 22, 2007.
  • Asthma and Allergy Foundation of America. Asthma. Accessed March 22, 2007.
  • Centers for Disease Control. Surveillance for Asthma - United States, 1960-1995, MMWR. 1998; 47 (SS-1). Accessed March 22, 2007.
  • Natural Standard: The Authority on Integrative Medicine. Copyright © 2007. Accessed March 22, 2007.
  • Ohio State University Medical Center. Peak Flow Meter. Accessed March 22, 2007.

Copyright © 2011 Natural Standard (


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Professor Keertan Dheda has received of several prestigious awards including the 2014 Oppenheimer Award, and has published over 160 peer-reviewed papers and holds 3 patents related to new TB diagnostic or infection control technologies. He serves on the editorial board of the journals PLoS One, the International Journal of Tuberculosis and Lung Disease, American Journal of Respiratory and Critical Medicine, Lancet Respiratory Diseases and Nature Scientific Reports, amongst others.Read his full biography at the University of Cape Town Lung Institute

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