Updated on March 31, 2025.
Asthma is a lung condition that can cause inflammation in your airways, making it difficult to breathe. If you’re having trouble getting—and keeping—your asthma under control, your healthcare provider (HCP) may recommend measuring your peak flow to help you better manage your condition.
What is a peak flow measurement?
“Peak flow is basically a way of measuring the maximum amount of air that can be exhaled very quickly as a person is breathing out after they have inhaled,” says Matthew Madden, MD, an internist in Charleston, South Carolina.
This measurement—also known as peak expiratory flow or peak flow rate—can provide insight into how well your lungs are working. A higher peak flow measurement typically means you’re managing well. A lower peak flow measurement suggests that your airways are narrowing due to asthma.
There’s no “normal” measurement to strive for. Instead, you work with your HCP to determine how the test can most accurately describe your condition.
Who should measure peak flow?
While measuring peak flow can be helpful for many people with asthma, it’s important to recognize that it’s not for everyone.
According to guidelines from the National Heart, Lung, and Blood Institute, your HCP may recommend peak flow monitoring if you:
- Have moderate or severe persistent asthma
- Have a history of severe asthma attacks
- Have difficulty pinpointing your asthma symptoms
- Have difficulty identifying your asthma triggers
- Have difficulty understanding the signs that your asthma is worsening
People who meet these criteria will typically use peak flow to establish an initial baseline measurement. Then, Dr. Madden explains, once their asthma is being managed well, people with asthma typically use peak flow measurement in the case of flare-ups—when they experience symptoms like wheezing or shortness of breath and want to know if it’s their asthma or something else.
How to use a peak flow meter
If it makes sense to measure peak flow as part of your asthma treatment plan, doing so is relatively simple with a small device called a peak flow meter. While there are several types of meters, they all generally work the same way to gauge your ability to quickly push air out of your lungs. Your HCP will recommend the best one for you.
“It’s important to know how to use a peak flow meter appropriately,” says Madden. A nurse or a respiratory therapist will typically teach you how to use the meter. Then they will observe you using it to make sure you’re getting an accurate measurement.
To best measure your peak flow, be sure to follow these steps at the same time each day:
- Remove any food, gum, or candy from your mouth.
- Set the scale on your meter to zero, or all the way down to the bottom.
- Sit or stand up straight.
- Take a deep breath and fill your lungs with air.
- While holding your breath, insert the mouthpiece into your mouth between your teeth. Close your lips tightly around it and keep your tongue from obstructing the opening.
- Blow all of the air out of your lungs as hard and fast as you can in one single, quick blow (no more than 2 seconds).
- Mark down the number on your meter’s scale.
For the most accurate readings, the American Lung Association recommends that you repeat this routine until you get three consecutive numbers that are close together. Then mark down the highest number of those three (known as your personal best) on your asthma action plan so you can share your results with your HCP at your next checkup.
Ask your HCP what time of day you should measure your peak flow rate. Also ask whether you should do it before taking medication, afterward, or both. Be sure to follow those instructions each time.
You should also be sure to use the same peak flow meter with each reading. If you get a new meter, you’ll likely have to work with your HCP to establish a new personal best. It’s a good move to bring your meter to your checkups and to consult with your HCP on the best ways to keep it clean and in working order, as well.
Understanding your peak flow readings
Your personal best peak flow measurement will become the baseline that you measure against, says Madden. This baseline should be established when you’re feeling well, rather than during an asthma flare up.
Once you’ve worked with your HCP to establish your baseline, it’s important to understand how to interpret your peak flow readings, which fall into three zones: green, yellow, and red. An easy way to gauge how well you’re doing is to think of a traffic light.
Green
When your peak flow measurement is between 80 and 100 percent of your baseline measurement, everything is a “go.” This means your asthma is being managed well and no changes to your day-to-day treatment plan need to be made.
Yellow
When your peak flow measurement is between 50 and 79 percent of your baseline, you may want to “proceed with caution.” This means your airways are narrowing and you may require additional treatment. Talk to your HCP about what changes should be made to your treatment plan when you’re in the yellow zone and include those instructions in your asthma action plan.
Red
When your peak flow measurement is less than 50 percent of your baseline, you should “stop,” treat your asthma with your emergency medications, and seek immediate medical attention. Talk to your HCP about what exact steps you should take when you’re in the red zone and include those instructions in your asthma action plan.
You’ll want to work with your HCP to determine which treatment to administer for each zone and when to seek medical care. “Your physician can give you instructions based on the measurements you’re getting or any breathing difficulties you’re having,” says Madden.
The benefits of measuring peak flow
If you and your HCP decide to add peak flow measurement to your asthma action plan, tracking these readings over time can help you:
- Identify asthma triggers so you know what to avoid
- Determine how well your asthma treatment plan is working
- Make any necessary treatment adjustments
- Develop a plan for when to seek emergency medical care
- Better understand how your asthma is affecting you
What’s more, measuring your peak flow rate over time can help you identify and address changes in your airways before asthma symptoms really set in. This can help you prevent a full-on flare up.
“When peak flow measurements are included as part of a comprehensive asthma action plan," says Madden, “patients can experience an improved quality of life in terms of decreased asthma symptoms overall and the ability to keep asthma at baseline.”
