A peak flow meter is a device used to measure peak flow. Peak flow is how much air you breathe out when trying your hardest. Checking your peak flow can tell you how well your lungs are working. It helps you know if your asthma is staying the same, getting better, or getting worse.

Peak flow meters come in many shapes and sizes, but they work about the same. Follow these steps to measure your peak flow.

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  Find your personal best peak flow. Keep a diary of your peak flow when your asthma is under control. Your doctor will let you know how long to do this. Your personal best peak flow is the highest number in your diary.

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  Work with your doctor to make an asthma action plan. Your doctor will add peak flow numbers to each zone in your action plan. The numbers are based on your personal best peak flow.

  • You're in the green zone when your peak flow number is close to your personal best. It's where you want to be.
  • You're in the yellow zone when your peak flow number is much lower than your personal best. Your asthma may be getting worse.
  • You're in the red zone when your peak flow number is very low. It means danger. Get medical help.

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  Check your peak flow, and find which zone you're in. Or you can use your symptoms along with your peak flow to find the zone you're in. Check your peak flow as often as your doctor recommends.

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  Follow the steps in your action plan for the zone you're in. This can include what medicine to take and when to call for help.

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  Recheck your personal best peak flow now and then. Ask your doctor how often to recheck it. If it has changed, the numbers on your action plan may need to be changed.