Children's Asthma Peak Flow Calculator
This calculator is for children with asthma. If you know your child's height, you can find his or her predicted
peak flow meter value. Peak flow is how fast your child exhales 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. Changes from
child's personal best can help you see how well your child's asthma is under control. These changes also can let
know when your child needs medication and when your child needs medical care.
If you don't know how to find it, click here for an
Note: The minimum height for this calculator is 44 inches.
Instructions for Determining 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
to three weeks. You should take these measurements only when your child's asthma is in good control.
Good control means your child doesn't currently have any symptoms of asthma.
Each person's asthma is different, and each person's personal best peak flow number is different.
Children's peak flow numbers typically vary by height, but even among people of the same height, weight
and sex, peak flow numbers can differ.
Here's how to determine your child's personal best peak flow number:
- Take peak flow readings at least two times a day for two to three weeks.
- Take the readings when your child wakes up and again between noon and 2 p.m.
- If your child uses quick-relief medication, take the readings before and after your child uses this
Talk with your child's doctor before measuring your child's personal best peak flow number. He or she
other instructions or suggestions, based on your child's condition.
Once you know your child's personal best peak flow number, you can use this calculator or ask your
to help determine the values for your child's Green, Yellow and Red Zones.
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Since your child's height is , his or her estimated peak flow meter value is .
What are asthma zones?
How much your child's daily peak flow differs from his or her personal best is
described as being in the Green, Yellow, or Red Zone. Here is a breakdown of each zone.
- The Green Zone
is 80 to 100 percent 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 medication as
- The Yellow Zone is 50 o 79 percent of your child's personal best. It is your child's caution
signal. It means your child needs to take his or her quick-relief medicine from the instructions on your child's
written asthma plan of action. The Yellow Zone also means your child's asthma may not be in good control. Ask
your child's doctor if your child needs to change or increase his or her daily medications.
- The Red Zone
is less than 50 percent of your child's personal best. It is your child's emergency signal. Your child should
take or increase his or her quick-relief medicine immediately, according to the instructions on your child's
written plan of action. Then, call your child's doctor to find out what to do.
This calculator is not intended to replace the evaluation of a health care professional.