• Topics: Family Youth and Community Sciences | Shelnutt, Karla P | Chan, Lisa (student) | Obesity and Overweight | Raising Healthy Children series

Raising Healthy Children: BMI Charts¹

Growth charts have been used to monitor the growth of infants, children and adolescents in the United States for over 30 years. These charts provide growth curves for weight, length/stature (height) and head circumference. 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 (2000) is the inclusion of body mass index (BMI) for age and sex.

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

Growth Charts

Parents often wonder whether their children are growing at a normal rate and are at the “right” height and weight for their age. Growth charts are used to compare a childs size and pattern of growth with a nationally representative reference sample of children the same age and sex. Pediatricians use the charts at each well-child visit to document childrens growth. This helps them to identify major changes in a childs 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 also recommends calculating and plotting BMI for age and gender starting at age two to screen for overweight and obesity. BMI charts are publicly available to consumers, and you can use them to track your childs 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 individuals weight in kilograms (kg) by the individuals height in meters (m) squared, or weight in pounds (lb) multiplied by 703, divided by height in inches (in) squared.

An easy way to determine BMI is to use a BMI calculator available online. The National Heart, Lung and Blood Institute has a BMI calculator available at: http://www.nhlbisupport.com/bmi/.

Measuring Height and Weight

To measure your childs height and weight accurately at home, follow these simple instructions:

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 × 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 be wearing light clothing such as a t-shirt and shorts and be barefoot.

• Have child stand in the center of the scale and remain still until weight has been read. Measure 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

85lb ÷ 2.2 lbs/kg = 38kg

Using the BMI Charts

There are different BMI-for-age charts for boys and girls and both are available on the CDC website http://www.cdc.gov/growthcharts/clinical_charts.htm. Here you can see what these charts look like for girls and boys.

Figure 1. 

Sample BMI charts (body mas index-for-age)

[Click thumbnail to enlarge.]

Plotting the BMI value on the BMI-for-age chart will show you your childs 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 childs age along the bottom of the chart (the X-axis). Use a straight edge to make a vertical line going up through the chart. Next, find your childs 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 will meet on one of the curved percentile lines and sometimes between two of the curved percentile lines printed on the chart. For example, the childs 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.

MyPyramid for Preschoolers BMI Charts

Parents of preschoolers ages two to five have an even easier way to plot their childs BMI by entering their childs information into the MyPyramid for Preschoolers “Preschooler Growth Charts” Web page located at http://www.mypyramid.gov/preschoolers/Growth/index.html. This site allows parents to personalize the growth chart with their childs name. Below is an example of what these charts look like:

Figure 2. 

Sample BMI chart using the MyPyramid.gov personalization feature

[Click thumbnail to enlarge.]

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.

While BMI charts are useful for screening and monitoring childrens 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 childs BMI, make an appointment with your childs 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. If there are indications that your childs weight status may put him or her at risk for diseases like diabetes and heart disease, your pediatrician also may order other tests, such as blood tests, and ask about diet and family history.

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

Frequently Asked Questions

How quickly should my child be growing? What determines this?

Children's growth is influenced by many factors including genetics, the childs diet and exercise habits, the childs 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 childs pediatrician or primary healthcare 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 childs 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 childs pediatrician to discuss these concerns. S/he will be able to help determine the cause of your childs slowed growth.

Learn More

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

• Cooperative Extension Family and Consumer Sciences (FCS) Educator (look in the blue pages of your phone book). Florida Extension offices are listed online by UF/IFAS at http://SolutionsForYourLife.com/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

Centers for Disease Control and Prevention. This site gives information about children's BMI and how to calculate and interpret the BMI. http://www.cdc.gov/healthyweight/assessing/bmi/childrens_bmi/about_childrens_bmi.html

KidsHealth from Nemours. This site provides information for parents, teens, and kids on growth charts and provides frequently asked questions about growth. http://kidshealth.org/parent/growth/growth/growth_charts.html#

National Heart, Lung, and Blood Institute. This site gives information on calculating BMI and on maintaining a healthy weight. http://www.nhlbi.nih.gov/health/public/heart/obesity/wecan/healthy-weight-basics/body-mass-index.htm

Department of Health and Human Services; National Institutes of Health. Provides an adult BMI calculator. http://www.nhlbisupport.com/bmi/

National Library of Medicine. This article, “Age appropriate diet for children”, gives advice on types of foods children of each age should be eating. http://www.nlm.nih.gov/medlineplus/ency/article/002455.htm

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 extension publications, contact your county Cooperative Extension service.

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

• Copyright 2012 |
• Site Feedback |
• About This Site