A peak flow meter helps you check how well your asthma is controlled. Peak flow meters are most helpful for people with moderate or severe asthma.

This guide will tell you (1) how to find your personal best peak flow number, (2) how to use your personal best number to set your peak flow zones, (3) how to take your peak flow, and (4) when to take your peak flow to check your asthma each day.

Starting Out: Find Your Personal Best Peak Flow Number

To find your personal best peak flow number, take your peak flow each day for 2 to 3 weeks. Your asthma should be under good control during this time. Take your peak flow as close to the times listed below as you can. These times for taking your peak flow are only for finding your personal best peak flow.

  • Between noon and 2:00 p.m. each day
  • Each time you take your quick-relief medicine to relieve symptoms (measure your peak flow after you take your medicine).
  • Any other time your doctor suggests.

Write down the number you get for each peak flow reading. The highest peak flow number you had during the 2 to 3 weeks is your personal best.

Your personal best can change over time. Ask your doctor when to check for a new personal best.

To check your asthma each day, you will take your peak flow in the morning. See below for more on how to take your peak flow.

Your Peak Flow Zones

Your peak flow zones are based on your personal best peak flow number. The zones will help you check your asthma and take the right actions to keep it controlled. The colors used with each zone come from the traffic light.

Green Zone (80 to 100 percent of your personal best) signals good control. Take your usual daily long-term-control medicines, if you take any. Keep taking these medicines even when you are in the yellow or red zones.

Yellow Zone (50 to 79 percent of your personal best) signals caution: your asthma is getting worse. Add quick-relief medicines. You might need to increase other asthma medicines as directed by your doctor.

Red Zone (below 50 percent of your personal best) signals medical alert! Add or increase quick-relief medicines and call your doctor now.