What Should My Peak Flow Be? - Asthma

June 13, 2022
Andrew Gallagher
3 Min Read

What is Peak Flow?

Peak Expiratory Flow Rate (PEFR) or just simply peak expiratory flow (PEF) or as I have read on reddit "peak flow" is a measurement used to analyse condition severity of people with asthma. It requires the patient to exhale as hard as they can through a device, the maximum speed of their exhale is the peak flow, measured in either Litres/Sec or Litres/Min. PEF is measured with a peak flow meter or a spirometer.

This guide should only give an indication of what your peak flow might be based on factors that effect peak flow, but each person should establish their own personal best and baseline values with the help of their doctor and then base their classifications off that.

Related article: Peak Flow Meter vs Spirometer

What is Peak Flow Used For?

Because your lung function may decrease before you notice any signs or symptoms of exacerbation, regularly measure and record your peak flow with a peak flow meter or spirometer.

What Factors Influence a Persons Peak Flow?

Peak flow readings are based on a variety of factors:

  • Height
  • Sex
  • Race
  • Age
  • Condition Severity

What Should My Peak Flow Be?

Below there is a calculator for the average peak flow based on the factors above:


The number of your peak flow itself does not matter, what matters is the change. If your peak flow rapidly decreases it may be alerting you to an attack.

Peak Flow Classification

There are 3 classifications of peak flow:

Greater than 80% of your predicted or personal best peak flow:

  • Your disease is under control - enjoy the day!

Between 50 - 80% of your predicted or personal best peak flow:

  • Your airways are narrowing
  • Your condition may not be under control
  • Take rescue medicine - if it doesn't bring relief, the symptoms are worsening, or you're back in the yellow zone in 4 hours - contact your doctor

Less than 50 % of your predicted or personal best peak flow:

  • Your airways are severely narrowed
  • Use an emergency medicine and contact professional health care immediately!

Although this classification system does come with a warning, if your peak flow is within normal ranges but you feel unwell (tight chest, shortness of breath, trouble speaking etc. ) you should consult with your doctor.

Related article: Shortness of Breath? - It May Not Be Your Asthma Symptoms

What Should I do If my Peak Flow Decreases Suddenly ?

Your peak flow will decrease if you are having an exacerbation, the further it is from your baseline the more severe your attack is.

When your peak flow measurements decrease and alert you to an oncoming attack, take your medication as instructed. Also, immediately stop any activity that may have triggered the attack. If your symptoms don't improve, get medical help as directed in your action plan.

Peak Flow Chart

Asides from a calculator to get your value of normal peak flow, you can also use a chart. It doesn't take race into account but is used by medical experts, mainly in Europe.

peak flow chart

Some people also use a peak flow diary, this enables them to record daily peak flows over time and monitor them.

You can find the usable version of this here - make a copy and make it your own.

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