Peak Flow Meter

For people with asthma or certain other breathing problems, a peak flow meter is a simple but important tool to help with daily asthma management. A peak flow meter is an easy-to-use device that measures how well your lungs are working. Peak flow meters are available over-the-counter.

The readings from the meter will help you and your caregiver:

  • Determine the severity of your asthma.

  • Evaluate the effectiveness of your current treatment.

  • Determine when to add or stop certain medicines.

  • Recognize an asthma attack before signs or symptoms appear.

  • Decide when to seek emergency care.

Your "personal best"

Your "personal best" is the highest peak flow rate you can reach over a 2-3 week period when you feel good and have no asthma symptoms. Your flow rate serves as a benchmark in your daily self-management plan. Because everyone's asthma is different, your personal best will be unique to you.

Your caregiver will help you figure out your personal best. Typically, you will take readings once or twice a day for 2 weeks when you are not having symptoms. The highest consistent reading during the trial period is your "personal best."


  1. Move the upper marker to the number that is your "personal best."

  2. Move the lower marker to the bottom of the numbered scale.

  3. Connect the mouthpiece to the peak flow meter.

  4. Stand up.

  5. Take a deep breath. Fill your lungs completely.

  6. Place your lips tightly around the mouthpiece. Blow as hard and as fast as you can with a single breath.

  7. Note the final position of the lower marker. This is your peak flow rate.

  8. Move the lower marker back to the bottom of the numbered scale.

  9. Repeat these steps 2 more times. Record the highest reading of the 3 tries in your asthma diary.

For the most accurate readings, it is important to keep your peak flow meter clean. Follow the manufacturer's instructions on how to take care of your peak flow meter.


You and your caregiver can use color coded "zones" on the meter to see how your peak flow rate compares to your "personal best." The color code for each zone reflects progressively more severe symptoms:

Green zone = stable

  • Your peak flow rates are 80 to 100 percent of your personal best. This means that your asthma is under control.

  • You probably have no asthma signs or symptoms.

  • Take your preventive medications as usual.

Yellow zone = caution

  • Your peak flow rates are 50 to 80 percent of your personal best. This means that your asthma is getting worse and could be improved.

  • You may have signs and symptoms such as coughing, wheezing or chest tightness. However, your peak flow rates may decrease before symptoms appear.

  • You may need to increase or change your asthma medication.

Red zone = danger

  • Your peak flow rates are less than 50 percent of your personal best. This means that you may be in danger of a medical emergency.

  • You may have severe coughing, wheezing and shortness of breath. Stop whatever you are doing. Use your rescue inhaler (for example, albuterol) or other medicines to open your airways.

  • Your asthma action plan will help you decide whether to call your caregiver or seek emergency care.

If your flow readings fall too far below your personal best into the yellow or red zone you'll need to take action to prevent or minimize an asthma attack.


  • Breathing too quickly may cause dizziness. At an extreme, this could cause you to pass out. Take your time so you do not get dizzy or light-headed.

  • If your lips are not placed tightly around the peak flow meter mouthpiece, you will get incorrect low readings.


  • Rest and breathe slowly and easily.

  • Keep a record of your progress. Your caregiver can provide you with a simple table to help with this.


Your caregiver will give you instructions on when to do regular monitoring. You may also need to check your peak flow when:

  • Asthma symptoms wake you up at night.

  • You have increased symptoms during the day.

  • You have a cold, flu or other illness that affects your breathing.

  • You need quick relief "rescue medication." (If possible, check your peak flow before you use rescue medication. Check it again 20 or 30 minutes after taking medication.)