Peak Flow Meter

A peak flow meter is a simple, easy-to-use device that measures how fast you can exhale a lungful of air. It helps manage asthma and can even indicate when your asthma is getting worse before you have symptoms. Use your peak flow meter at least once a day or as directed by a healthcare provider.


A peak flow meter uses a traffic light system. Green is good, yellow means your flow is worsening and red is an emergency.
A peak flow meter measures the top speed you can blow air out of your lungs. It can help you recognize an asthma attack.

What is a peak flow meter?

A peak flow meter is a small, handheld device that measures how fast you can push air out of your lungs when you blow out (exhale) as hard and as fast as possible. This is your peak flow. Another name for peak flow is peak expiratory flow measurement.

There are manual and digital peak flow meters. A manual peak flow meter has markers on the device that you use to track your peak flow. A digital peak flow meter displays your peak flow on a screen.

Peak flow meters come with a chart with average readings. It’s important to remember that you don’t need to aim for these numbers — they’re just an average.

What condition does a peak flow meter help manage?

A peak flow meter helps manage moderate to severe asthma. It measures how open the airways (bronchi) are in your lungs. Your peak flow may drop, even before you have an asthma attack. A drop in your peak flow tells you that your asthma might be getting worse.


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Procedure Details

How do I use a peak flow meter?

A peak flow meter is simple to use. To measure your peak flow:

  • Sit or stand up straight. Standing up may make it easier to breathe deeply. Whichever you choose, make sure you do it this way each time you use a peak flow meter.
  • Make sure the marker is at the bottom of the meter.
  • Take a deep breath, filling your lungs completely, and hold it. A very deep breath will move your abdominal (belly) muscles, too, not just your chest muscles.
  • Put your mouth around the mouthpiece and close your lips tightly. Make sure your lips form a seal so no air escapes around the outside of the mouthpiece.
  • Blow all the air out of your lungs as hard and fast as possible in a single exhale.
  • Write down the number by the marker on the meter.

Repeat these steps three times. The highest of these three readings is your daily peak flow. Write down your daily peak flow on a sheet of paper, on your calendar, in your smartphone or in your asthma diary. You should also record:

  • Any symptoms you have, including wheezing, chest tightness, shortness of breath or coughing.
  • If you’ve taken your rescue inhaler or any other emergency medication (including bronchodilators or anti-inflammatory medicines).

What units does a peak flow meter measure in?

A peak flow meter measures liters per minute (L/min).

How do you find your “personal best” peak flow?

Your personal or usual best peak flow is the highest number you can achieve over a two-week period while your asthma is under good control. “Good control” means you feel good and don’t have any symptoms. You’ll compare your other peak flow readings to your best peak flow number.

To find your personal best peak flow:

  • Perform peak flow testing twice a day for two weeks.
  • Test at the same time in the morning and early evening.
  • Perform the test before taking any inhalers or as instructed by a healthcare provider.

Once you determine your personal best peak flow, continue using your peak flow meter daily or as instructed by a healthcare provider. Regularly using your peak flow meter will help you recognize decreases in your airflow early. This can help guide your asthma treatment. A provider may use these numbers to create an asthma action plan to help manage your symptoms.

What is a normal peak flow meter reading?

It depends. Your “normal” peak flow may differ from another person’s “normal” peak flow. A healthcare provider will help determine your normal peak flow according to your:

  • Age. Children have smaller lungs than adults.
  • Height. The taller you are, the bigger your lungs.
  • Sex. People assigned male at birth (AMAB) usually have bigger lungs than people assigned female at birth (AFAB).

Healthcare providers generally use a “traffic light” system that consists of three zones to determine your peak flow rate:

  • Green zone. Your asthma is in good control. Your peak flow is 80% to 100% of your personal best.
  • Yellow zone. Your asthma isn’t in good control or is getting worse. Your peak flow is 50% to 80% of your personal best.
  • Red zone. Your asthma is severe. Your peak flow is less than 50% of your personal best. You need emergency care.

To find the number ranges for your zones, multiply your personal best peak flow by:

  • (100%).
  • 0.8 (80%).
  • 0.5 (50%).

Record these ranges so you can reference them quickly. For example, if your personal best peak flow is 400 L/m, the zones will be:

  • Green zone: 320 to 400 L/m (80% to 100%).
  • Yellow zone: 200 L/m to 320 L/m (50% to 80%).
  • Red zone: Less than 200 L/m (less than 50%).

If you’re in the yellow or red zones, you must adjust your medicine according to your healthcare provider’s instructions. Use the peak flow values and your symptoms to take action, if necessary. If you have an asthma action plan, make sure you understand and can follow it. Ask a healthcare provider if you have any questions.

What should your lung capacity be on a peak flow meter?

Your peak flow will vary according to your age, height and sex. Peak flow numbers are usually higher in people who are younger, taller or AMAB.

A normal peak flow in adults may be between 400 and 700 L/m. In children, a normal peak flow may range from around 150 to 450 L/m. Be sure to keep track of your peak flow readings. A healthcare provider can use this information to observe your numbers over time and determine if your results are changing.

What is a bad peak flow meter reading?

If your peak flow is in the yellow or red zones, immediately use your rescue inhaler or other emergency medications. If your peak flow doesn’t improve, call a healthcare provider immediately or go to the nearest emergency room.

Is 250 on a peak flow meter good?

It depends. A reading of 250 L/m may be good for some people but not others. Talk to a healthcare provider if you have questions about your peak flow meter readings.

Risks / Benefits

What are the potential benefits of this treatment?

Measuring your peak flow can help you:

  • Learn what causes or triggers a flow drop.
  • Decide which asthma medications to use.
  • Recognize when you need emergency care.


What are the risks or complications of a peak flow meter?

In general, a peak flow meter is safe and easy to use. However, risks may include:

  • Feeling dizzy or lightheaded (presyncope) from taking deep breaths.
  • Wheezing or coughing fits.
  • Not breathing in deeply enough or blowing out strongly enough to get an accurate reading.

You also run the risk of getting an inaccurate reading if you take asthma medication before you use a peak flow meter.

Using the same peak flow meter is important to get the most accurate measurements. Different peak flow meter brands may use different measurements.

When To Call the Doctor

When should I call a healthcare provider?

If your peak flow is in the yellow zone, call a healthcare provider immediately and take asthma medications. If it’s in the red zone, take rescue medicine right away and call a provider or get to the nearest emergency room if your symptoms don’t improve.


Additional Common Questions

What is the difference between a spirometer and a peak flow meter?

A spirometer is a machine that measures lung capacity. That means the amount of air you can inhale into, and exhale out of, your lungs. A peak flow meter measures how fast you can push air out of your lungs.

A note from Cleveland Clinic

A peak flow meter helps you manage asthma and recognize changes in how well you’re breathing. It may be challenging to know if you’re using it correctly. A healthcare provider will demonstrate how to use it and ensure you use it properly. It’ll give you a good idea of your average peak flow. Your numbers may vary a little bit. But if there are any significant drops in your numbers, use your rescue inhaler or any other medications and call a healthcare provider immediately or get emergency care.

Medically Reviewed

Last reviewed on 04/29/2024.

Learn more about our editorial process.

Appointments 216.444.6503