Skip To Content

All About Your Peak Flow Meter

Match up your peak flow with your asthma action plan to help with optimal control.

By Emily Gurnon, Contributing Writer

Your peak flow meter tells you how well your lungs are working at any given time. It is a measure of how well air moves out of your lungs. It can warn you of an asthma attack even when you feel okay and before you have symptoms. It can also help assess how well your medicine is working to control your asthma.

Who should use one?
A peak flow meter is recommended if you have moderate to severe asthma. It is also recommended if you are adjusting your daily asthma medication, if you have trouble discerning whether or not you’re having symptoms, or if your symptoms are worsening. You may also use the device if your symptoms are affected by certain environmental or work conditions. Ask your doctor if a peak flow meter would be helpful for you.

When should I use it?
How often you use your peak flow meter depends on a number of factors. For example, you may be advised to measure your peak flow only when your symptoms get worse. Or if you may need to measure your peak flow a daily, even if you’re not having symptoms. Some people may need to measure their peak flow a number of times each day. Talk to your doctor about what is best for you.

How do I use a peak flow meter?
First, you will need to find your personal best in peak flow results. This is the highest peak flow number you can reach during a two-week period when you feel good and don’t have any asthma symptoms. To determine this number, you should use your meter every day for two to three weeks when your asthma is under control. Share the readings with your doctor.

To use the meter:

  1. Move the indicator to the bottom of the numbered scale.
  2. Stand up straight.
  3. Take a deep breath, filling up your lungs completely.
  4. Put your mouth on the mouthpiece, and make sure your lips are closed tightly around it. (Keep your tongue away from the mouthpiece.)
  5. Breathe out as hard and fast as you can in a single blow. As you exhale, you will see a marker move along a scale with numbers on it.

After you use the meter, write down the result. Do the same procedure two more times, making note of each result. Record the best of the three results on your peak flow chart.

Once you know your personal best, you and your doctor can determine how well your asthma is controlled by monitoring the peak flow results over time.

Peak flow and your asthma action plan
Tracking the peak flow levels is an important part of your asthma action plan. An action plan, devised by you and your doctor, gives you guidance on avoiding asthma triggers, how to take your medicines the right way, what to do if your symptoms get worse and when to seek emergency care.

Asthma action plan, peak flow and the color zones
The asthma action plan uses a set of standardized color zones to help you identify whether you are doing well, getting worse or are in need of immediate medical help. Your doctor can tell you which peak flow levels correspond to the three zones for you.

  • Green zone: Your number is 80 percent or more of your best peak flow. You are not having symptoms and can do your usual activities. You should keep taking your regular long-term medicines.
  • Yellow zone: Your number is 50 to 79 percent of your best peak flow. Usually, symptoms have appeared. You can do some of your usual activities, but not all. This is a time to take action. Follow the directions in your asthma action plan regarding medications and what to watch for.
  • Red zone: Your number is less than 50 percent of your best peak flow. This indicates a medical emergency. You may be very short of breath and cannot do your usual activities. Do as your plan advises and seek emergency help if necessary. Your plan will advise to use your quick-relief/rescue medicines until you get help. If you can’t walk or talk due to shortness of breath, your symptoms are severe and worsening, or if you lips or fingernails are blue or gray, call 911!

Your asthma action plan will be tailored especially for you. Both you and your family can benefit from having its information and guidance in one place.


National Heart, Lung, and Blood Institute. Expert panel report 3: Guidelines for the diagnosis and management of asthma. Accessed: January 20, 2016.
National Heart, Lung, and Blood Institute. How is asthma treated and controlled? Accessed: January 20, 2016.
American Lung Association. Measuring your peak flow rate. Accessed: January 20, 2016.

Last Updated: January 29, 2016