Search Encyclopedia

Children's Asthma Peak Flow Calculator

This calculator is for children with asthma. If you know how tall your child is, you can find out what their estimated personal best peak flow value should be. Peak flow is how fast your child breathes out air after taking a deep breath. Your child's peak flow tells you and your child's healthcare provider how well your child's lungs are working.

You need to know your child's personal best peak flow number to help control your child's asthma. This number is part of your child’s Asthma Action Plan.

Changes from your child's personal best can help you see how well your child's asthma is under control. These changes also can let you know when your child needs medicine and when your child needs medical care.

If you don't know how to find your child's personal best peak flow, click here for an explanation.

Note: The calculator will only work if your child is between 43 inches and 65 inches tall.

How to find your child's personal best peak flow number

Your child's personal best peak flow number is the highest peak flow number your child can measure 2 to 4 times every day over 2 to 3 weeks. Your child's healthcare provider will tell you if you need to measure peak flow for longer than 2 to 3 weeks.

It is very important to know what your child’s "baseline" peak flow is. This baseline is done when your child is feeling well and their asthma is in good control. Good control means your child doesn't currently have any symptoms of asthma.

Each child's asthma is different. And each child’s personal best peak flow number is different. Children's peak flow numbers typically vary by height. But even among children of the same height, weight, and sex, peak flow numbers can be different.

Here's how to find out your child's personal best peak flow number:

Use the same peak flow meter for each reading.
Take peak flow readings at least 2 to 4 times a day for 2 weeks. Your child's healthcare provider will tell you if you need to measure peak flow for longer than 2 weeks.
Set the device to zero or its base level.
Your child should remove any gum or food from their mouth.
Take peak flow reading when your child is standing. If your child cannot stand, have your child sit up straight.
Have your child put their tongue under the mouthpiece when the meter is in your child’s mouth. It’s important that your child keep their tongue away from the mouthpiece.
Your child should close their lips tightly around the mouthpiece.
Your child should blow out as hard and fast as possible. Your child should not throw or lean their head forward as your child blows the air out.
Your child should take a few normal breaths and then repeat the process 2 to 3 more times.
Write down the highest of the 3 measurements. Never average the numbers. The highest reading is your child's personal best peak flow.
Take your child's measurements at the same time each day. Ask your child’s healthcare provider about the best time to do this.
If your child uses quick-relief medicine, take the readings before or after your child uses this medicine, or both. Ask your child’s healthcare provider about the best time to do this.

Keep a chart of your child's peak flow measurements. Share this with your child's healthcare provider during routine checkups and as needed.

Be sure to clean the peak flow meter. Follow the meter's cleaning instructions. Dirt collected in the meter may not give a correct peak flow measurement. Germs or mucus can get inside the peak flow meter if your child has a cold or other respiratory infection. That’s why it's important to keep the meter clean.

Close this section

Enter your child's information

What is your child's height? inches

Your child's results

Because your child's height is , their estimated peak flow is .

About asthma

Asthma is a long-term (chronic) disease. Making sure that your child’s asthma is under control is a team effort. Your child and their caregivers are important team members.

One of the key parts of controlling asthma is having an Asthma Action Plan. You will develop this plan with the help of your child’s healthcare provider. Each person who cares for your child will need to have a copy of this plan. The plan is just for your child. Don’t use a plan created for someone else.

An Asthma Action Plan gives step-by-step instructions on what to do if your child has asthma symptoms. The plan helps reduce or prevent asthma flare-ups. It also helps keep your child out of the ER and the hospital. The plan tells you and your child what symptoms to watch for. It tells you how to treat those symptoms right away. This will also help stop flare-ups from getting worse. The plan will also tell you when to seek emergency care.

Part of your child’s Asthma Action Plan is watching their peak flow. You need to know how to use a peak flow meter. You also need to know what to do based on the meter’s readings.

Using the peak flow meter

Check your child's peak flow measurement when the following symptoms appear, unless your child's healthcare provider tells you otherwise:

Coughing
Wheezing
Shortness of breath

Talk with your child's healthcare provider before measuring your child's personal best peak flow number. They may have other instructions or suggestions, based on your child's condition. Also show the provider how you or your child uses the peak flow meter. This will help you be certain that you are using correctly.

What are asthma action zones?

Your child’s Asthma Action Plan tells you what the values should be for your child's Green, Yellow and Red Zones. These zones tell you how much your child's daily peak flow differs from their personal best. It is important to follow your child’s Asthma Action Plan when his or her peak flow measurement falls in each of these zones. Always follow your child's Asthma Action Plan when acting on your child's peak flow measurements.

Here is a breakdown of each zone:

The Green Zone is 80% to 100% of your child's personal best. It is a sign that your child's asthma is in good control. It means your child currently has no symptoms of asthma. Your child should continue to take their medicine as usual.
The Yellow Zone is 50% to 80% of your child's personal best. The Yellow Zone number is your child's caution signal. It means your child needs to take their quick-relief medicine. The instructions will be in your child's Asthma Action Plan. The Yellow Zone also means your child's asthma may not be in good control. After your child recovers, call your healthcare provider to see if your child needs to change or take more of their daily medicines.
The Red Zone is less than 50% of your child's personal best. The Red Zone number is your child's emergency signal. Your child should take or take more of their quick-relief medicine right away. Follow the instructions in your child's Asthma Action Plan. Then call your child's healthcare provider to find out what to do. If your child's peak flow range does not return to the Yellow or Green Zone within the time expected, call 911. Also call 911 if your child’s Red Zone symptoms get worse.

Note: The numbers may be different for children ages 5 to 11. Talk with your child’s healthcare provider to find what peak flow ranges are normal. Follow the peak flow instructions in your child’s Asthma Action Plan.

This calculator is not intended to replace the evaluation of a healthcare professional.

Medical Reviewers:

Brennan, Dan, MD

Gotwals, Jessica RN BSN MPH

Pederson, Deborah, MD