University of FloridaSolutions for Your Life

Download PDF
Publication #FCS8923

Raising Healthy Children: BMI Charts1

Lisa D. Chan and Karla P. Shelnutt2

Growth charts have been used to monitor the growth of infants, children, and adolescents for at least a century. These charts provide growth curves for weight, length/stature (height), and head circumference (Grummer-Strawn, Reinold, & Krebs, 2010). Health care providers use these charts as a clinical tool to assess the adequacy of growth in their patients.

A new feature of the revised Centers for Disease Control and Prevention (CDC) - National Center for Health Statistics growth charts is the inclusion of body mass index (BMI) for age and sex (Grummer-Strawn, Reinold, & Krebs, 2010).

BMI is based on height and weight. It is used to screen children (2 years and older) and youth for overweight and obesity (CDC, 2011). The BMI charts also can be used to identify children who are underweight. This publication explains how health care providers use BMI charts to screen for potential weight problems that could lead to chronic health conditions.

Figure 1. 
[Click thumbnail to enlarge.]

Growth Charts

Parents often wonder if their children are growing at a normal rate and are at the “right” height and weight for their age. Growth charts compare a child’s size and pattern of growth with a nationally representative reference sample of children the same age and sex (Grummer-Strawn, Reinold, & Krebs, 2010). Pediatricians use the charts at each well-child visit to document children’s growth. This helps them to identify major changes in a child’s growth patterns, which may indicate a potential health problem. Although most parents are familiar and comfortable with the traditional growth charts (i.e., weight and stature for age, weight for stature), the American Academy of Pediatrics and the CDC also recommend calculating and plotting BMI for age and gender starting at age two to screen for overweight and obesity (CDC, 2011). BMI charts are publicly available to consumers, and you can use them to track your child’s growth. The main topic of this publication is the BMI-for-age chart, which can be used easily as a screening tool at home.

BMI — What Is It?

BMI is a quick, easy, and inexpensive way to estimate body fatness. BMI is calculated by dividing an individual’s weight in kilograms (kg) by the individual’s height in meters (m) squared, or weight in pounds (lb) multiplied by 703, divided by height in inches (in) squared (CDC, 2011).

BMI = Weight (kg)/Height (m2) OR Weight (lb) x 703/Height (in2)

An easy way to determine BMI for your child or teen is to use the CDC’s BMI Percentile Calculator. The tool is available at http://apps.nccd.cdc.gov/dnpabmi/. More information on this tool is provided later in this publication under the heading “CDC’s BMI Percentile Calculator for Children and Teens.”

Measuring Height and Weight

To calculate your child’s BMI, make sure you measure their height and weight accurately. For children and teens, fractions of inches or pounds can make a big difference in BMI results.

To measure your child’s height and weight accurately at home, follow these simple instructions (CDC, 2011b):

Height

  • Make sure your child is not wearing shoes, a hat, hair clips, or braids.

  • Take the measurement with your child standing on an uncarpeted surface against a flat wall.

  • Have your child stand with feet together and heels, back, buttocks and head against the wall. Legs should be straight, and the child should look straight ahead.

  • Take a straight, flat item, such as a ruler, and place it at a 90 degree angle from the wall (makes an L-shape).

  • Lower the ruler so it is firm on the top of your child's head.

  • Using a pencil, mark the wall where the bottom of the ruler meets it. Then take a metal tape measure and measure from that mark to the floor. For accuracy, take the measurement to the nearest eighth of an inch or tenth of a centimeter (cm). For use with calculating BMI, divide height in centimeters by 100 to find height in meters; inches do not need to be converted for use in the standard equation. If you want to convert inches to centimeters, you multiply height in inches by 2.54, and then convert centimeters to meters.

Example conversion:

Height of 47 inches

47 in x 2.54 cm/in = 120 cm

120 cm ÷ 100 cm/m = 1.2 m

Weight

  • Place a digital scale on a hard, even surface.

  • Your child should wear light clothing such as a t-shirt and shorts and be barefoot.

  • Have your child stand in the center of the scale and remain still until weight has been read. Measure the weight to one decimal point if possible. For use with calculating BMI, measure weight in kilograms or convert pounds to kilograms. Divide weight in pounds by 2.2 to get weight in kilograms.

Example conversion:

Weight of 85 pounds

85 lb ÷ 2.2 lbs/kg = 38 kg

Using BMI Charts

There are different BMI-for-age charts for boys and girls. You can print these charts from the CDC website (http://www.cdc.gov/growthcharts/clinical_charts.htm), and they are available in a variety of languages. Here you can see what these charts look like for girls and boys.

Figure 2. 

Girls BMI chart.


Credit:

CDC


[Click thumbnail to enlarge.]

Figure 3. 

Boys BMI chart.


Credit:

CDC


[Click thumbnail to enlarge.]

Plotting the BMI value on the BMI-for-age chart shows you your child’s weight status compared to other children of the same age and sex. The charts are set up with ages listed along the bottom edge of the chart (2–20 years old) and BMI values listed along both the right and left edges of the chart.

To use the chart, first find your child’s age along the bottom of the chart (the X-axis). Use a straight edge to make a vertical line going up the chart. Next, find your child’s BMI along the right or left side of the chart (Y-axis). If your child is between two and 11 years old, it is easier to use the left side of the chart. If he or she is between 11 and 20 years old, use the right side of the chart. Place the straight edge where your child's BMI is and draw a line horizontally across the chart. Find the spot where the two lines meet. Sometimes the lines meet on one of the curved percentile lines and sometimes between two of the curved percentile lines printed on the chart. For example, the child’s age and BMI value may fall on the curved line marked as the 25th percentile, or it may fall between the curved lines marked as the 25th and the 50th percentiles.

CDC’s BMI Percentile Calculator for Children and Teens

Parents of children and teens can use the CDC’s BMI calculator to gather information about their child’s BMI. The calculator can be found at http://apps.nccd.cdc.gov/dnpabmi/Calculator.aspx. This tool allows you to enter accurate and current information for your child and then plots this information for you. The tool also provides you with information and visuals explaining what your child’s BMI means.

Understanding Percentiles

Percentiles tell you where your child falls in relation to other children. For example, if an eight-year-old boy has a BMI of 20, he would be at the 95th percentile for BMI. This means that out of 100 boys his age, 95 of them have a lower BMI. The percentiles can be used to categorize weight status for children using Table 1.

Table 1. 

Weight Category

Percentile

Underweight

Less than 5th percentile

Healthy Weight

5th percentile to less than the 85th percentile

Overweight

85th percentile to less than the 95th percentile

Obese

95th percentile to less than the 97th percentile

Source: CDC, 2011a

While BMI charts are useful for screening and monitoring children’s weight status, they should not be used to diagnose a child as underweight, overweight, or obese. Rather, they should be used to determine if further tests are needed to see if a child has an underlying condition that may be causing their weight to be above or below a healthy weight.

If you are concerned about the percentile category of your child’s BMI, make an appointment with your child’s pediatrician. Your pediatrician can determine if more accurate measurements of body composition such as skin fold measurements, dual x-ray absorptiometry (commonly called DeXA), or bioelectrical impedance should be done (CDC, 2011a). If there are indications that your child’s weight status may put him or her at risk for diseases such as diabetes and heart disease, your pediatrician also may order other tests, such as blood tests, and ask about diet and family history (CDC, 2011a).

Use the BMI charts to monitor your child’s growth and to keep an eye out for any weight concerns. The following are some frequently asked questions parents may have about their children’s growth.

Figure 4. 
[Click thumbnail to enlarge.]

Frequently Asked Questions

How Quickly Should My Child Be Growing? What Determines This?

Children’s growth is influenced by many factors including genetics, the child’s diet and exercise habits, the child’s overall health, etc. Every child is different, and this is the reason the "normal" range on weight, height, and BMI charts is so wide.

What Should I Do if My Child Is Below the 5th Percentile?

If your child falls below the 5th percentile, make an appointment with your child’s pediatrician or primary health care provider. This individual is in the best position to identify and treat any health conditions that could be causing your child to grow at a slower rate.

What Should I Do if My Child Is Above the 85th Percentile?

If your child falls into the overweight or obese (over 95th percentile) category, it is best to meet with your child’s pediatrician for further assessment.

What Should I Do if My Child Was in the Normal Range, But Has Fallen To a Lower Percentile on the Growth Charts?

If your child begins showing signs of slowing in growth, meet with your child’s pediatrician to discuss these concerns. S/he will help to determine the cause of your child’s slowed growth.

Learn More

To get more information about BMI charts, contact one of the following reliable sources in your county:

  • UF/IFAS Extension Family and Consumer Sciences (FCS) Educator (look in the blue pages of your phone book). UF/IFAS Extension offices are listed at http://solutionsforyourlife.ufl.edu/map.

  • WIC nutritionist at your county health department (also in the blue pages of your telephone book).

  • For referral to a registered dietitian (RD) in your area you can call the Florida Dietetic Association at (850) 386-8850 or check the yellow pages of your phone book.

Recommended Websites

References

Centers for Disease Control and Prevention (CDC). (2011a). About BMI for children and teens. Retrieved from http://www.cdc.gov/healthyweight/assessing/bmi/childrens_bmi/about_childrens_bmi.html

CDC. (2011b). About BMI for children and teens: Measuring a child’s weight and height accurately at home. Retrieved from http://www.cdc.gov/healthyweight/assessing/bmi/childrens_bmi/measuring_children.html.

Grummer-Strawn, L. M., Reinold, C. M., & Krebs, N. F. (2010). Use of World Health Organization and CDC growth charts for children aged 0–59 months in the United States. Department of Health and Human Services, Centers for Disease Control and Prevention.

Footnotes

1.

This document is FCS8923, one of a series of the Department of Family, Youth and Community Sciences, UF/IFAS Extension. First published: May 2010. Latest revision: July 2013. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Lisa D. Chan, former dietetic intern, Master of Science-Dietetic Internship Program, Food Science and Human Nutrition Department, and Karla P. Shelnutt, PhD, RD, assistant professor, Department of Family, Youth and Community Sciences; UF/IFAS Extension, Gainesville, FL 32611.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.