This calculator is for children with asthma. If you know how tall your child is, you
can find out what his or her personal best peak flow value is. 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 doctor 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
Note: The calculator will only work if your child is at least 43 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 three weeks. Your child's healthcare provider will tell you if you need
to measure peak flow for longer than 2 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 his or her 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. The peak flow meter should read zero
or its lowest reading when your child is not using it.
- 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.
- Your child should remove any gum or food from his or her 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 his or her tongue under the mouthpiece when the meter is in your
child’s mouth. It’s important that your child keep his or her tongue away from the
- Your child should close his or her lips tightly around the mouthpiece.
- Your child should blow out as hard and fast as possible. Your child should not throw
or lean his or her 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
- 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
Your child's results
Because your child's height is , his or her estimated peak flow is .
Asthma is a complicated disease. Making sure that your child’s asthma is under control
is a team effort. Your child and his or her 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 doctor. 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 his or her peak flow. You need
to know how to use a peak flow meter. You also need to know what to do based on the
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:
- Shortness of breath
Talk with your child's doctor before measuring your child's personal best peak flow
number. He or she 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 his or her 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
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 his or her 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 his or her 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 his
or her 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 his or her 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.