Understanding Growth Charts for Kids

What Those Height and Weight Percentiles Mean

Pediatrician checking height of girl
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Growth charts are a tool for tracking a child's physical growth and development. They help a pediatrician make sure a kid is gaining inches, putting on pounds, and increasing in head size (an indicator of healthy and normal brain development) at a rate that's typical for her age.

By charting a child's height, weight, and head circumference over time, these measurements also allow doctors and parents to see if a child is gaining weight more quickly than she's adding inches, or vice-versa—signs that she may be on track to becoming overweight or isn't eating as much as she should.;

Understanding Percentiles

When your doctor's child measures her height, weight, and head circumference, not only will he tell you the results in terms of inches and pounds, he'll also express what her percentiles are for each measurement.

The percentile number means that your child exceeds that percentage of children her age for that measurement. If she's in the 75th percentile for height, she's taller than 75 percent of other kids her age, for example. On the other hand, if she's in the 25th percentile for weight, she only exceeds 25 percent of children her age in weight.

Charting Your Child's Growth Yourself

If you'd like to keep an eye on how your little one is growing between doctor visits, you can find growth charts online to help you do that. The first step is to find the right chart. If your child is healthy and developing normally, you have a couple of choices depending on her age. For an infant or toddler (up to age 2), use the growth charts from the World Health Organization (WHO), which reflect an international standard that was developed in 2006.

If your child is 2 or older, look at the growth charts developed by the National Center for Health Statistics. These were updated and revised by the U.S. Centers for Disease Control and Prevention (CDC) in 2000.

Note that there also are growth charts for premature babies and children who are born with specific conditions, such as Down syndrome, Prader-Willi syndrome, achondroplasia, Marfan syndrome, and others.

The Magic Foundation offers specialized growth charts for children with Noonan syndrome, Turner syndrome, Russell-Silver syndrome, and more conditions.

Reading the Charts

Say you have a 2-year-old boy who weighs 30 pounds. To find out what his percentiles are, start by using the CDC growth chart for boys from birth to 36 months. This chart, like all the others, have the age at the top and bottom of the grid and length and weight at the left and right of the grid. Curves on the chart indicate the percentiles for length-for-age and weight-for-age.

  • Step A: Find the child's age at the bottom of the chart and draw a vertical line on the growth chart (from top to bottom). For this example, you would draw a line through 24 months (2 years).
  • Step B: Now find the child's weight on the right-hand side of the chart, 30 pounds in this example, and draw a horizontal line (from left to right).
  • Step C: Find the spot where these two lines intersect or cross each other.
  • Step D: Find the curve that is closest to this spot and follow it up and to the right until you find the number that corresponds to your child's percentile.

In this example, you can see that a 2-year-old boy who is 30 pounds is at the 75th percentile for his weight, meaning he weighs more than about 75 percent of boys his age, and less than 25 percent of other 2-year-old boys.

 

Finding a child's percentile is a little harder if the curve doesn't actually pass through the spot where age and weight come together. For example, if the boy in the example weighed 31 pounds you would use all of the same steps but also have to imagine a curve that is somewhere between the 75th and 90th percentiles, figuring that he was at about the 80th to 85th percentile.

If your child is above the 95th or below the 5th percentile, then you will not be able to find an exact percentile, except to say that he is above or below the growth chart, but you can use the same steps to plot your child's height and body mass index.

What Do Percentiles Mean?

It is important to understand that growth charts are best used to follow your child's growth over time or to find a pattern of his growth. Plotting your child's weight and height at different ages and seeing if he follows a consistent growth curve is more important than what his percentiles are at any one time.

Even if your child is at the 5th percentile for his weight (meaning that 95 percent of kids his age weigh more than he does), if he has always been at the fifth percentile, then he is likely growing normally. It would be concerning and it might mean there was a problem with his growth if he had previously been at the 50th or 75th percentile and had now fallen down to the fifth percentile.

Also, remember that children between the ages of 6 and 18 months can normally move up or down on their percentiles, but older children should follow their growth curve fairly closely.

Sources:

Centers for Disease Control and Prevention (CDC). "Use and Interpretation of the WHO and CDC Growth Charts for Children from Birth to 20 Years in the United States." May 2013.

Grummer-Strawn LM, Reinold C, Krebs NF. "Use of the World Health Organization and CDC Growth Charts for Children Aged 0-59 Months in the United States.MMWR Recomm Rep 2010; 59(RR-9);1-15.

Multicentre Growth Reference Study Group. "WHO Child Growth Standards: Growth Velocity Based on Weight, Length and Head Circumference: Methods and Development." 2009.