A peak flow meter is a portable, inexpensive, hand-held device that measures your ability to push air out of your lungs. Air flow is measured by the amount of air that you can blow out in one “fast blast.”

Peak flow meters come in two ranges to measure the air pushed out of your lungs. A low range peak flow meter is for small children, and a standard range peak flow meter is for older children, teenagers, and adults. An adult has much larger airways than a child and needs the larger range.

Who can benefit from a peak flow meter?

People with asthma can benefit from using a peak flow meter, and some people with chronic bronchitis and emphysema. A peak flow meter may be most beneficial for people that are newly diagnosed with asthma and those with persistent asthma. A peak flow meter can be an essential part of your asthma management plan if you need to adjust your daily medication for asthma.

A peak flow meter can be especially helpful to use with young children who may not be able to communicate about trouble breathing. Children as young as five are usually able to use a peak flow meter to help manage their asthma.

Determining a “Normal” Peak Flow Rate

Peak flow rates are commonly split into three zones. The colors of a traffic light – green, yellow, red – are used to represent the three zones. In general, a normal peak flow rate can vary as much as 20 percent.

Be aware of the following general guidelines. Keep in mind that recognizing changes from “normal” is important. Your healthcare provider may suggest other zones to follow.

Green Zone: 80 to 100 percent of your usual or “normal” peak flow rate signals all clear. A reading in this zone means that your asthma is in good control. Keep using the medicines as directed.
Yellow Zone: 50 to 80 percent of your usual or “normal” peak flow rate signals caution. This zone indicates that your airways are narrowing, and you need to take action. Take the additional medicine(s) listed in the yellow zone of your asthma action plan. Call your doctor and let them know.
Red Zone: Less than 50 percent of your usual or “normal” peak flow rate signals a medical alert. This zone indicates that there is severe airway narrowing. Take your quick-relief medicine right away. Contact your healthcare provider right away and if symptoms don’t improve, call 911 or go to the nearest emergency room.

Some healthcare providers may suggest zones with a smaller range, such as 90 to 100 percent. Always follow your healthcare provider’s suggestions about your peak flow rate.

*information from The American Lung Association