A peak flow meter is a portable handheld device used to measure how well a person with asthma can blow air out of the lungs. (Asthma narrows the airways, making breathing difficult.) The person blows into the meter and then checks the reading.

Some people with asthma use a peak flow meter at home to see how well their asthma is being controlled. The meter can tell if the airways are getting narrow even before symptoms start.

Peak flow measurements can help people with asthma work with their doctor to identify approaching asthma flare-ups, develop an asthma treatment plan, and know when to get medical care.