How to Read Growth Charts

Growth charts use percentile rankings to compare an infant's, child's or teenager's height-for-age and weight-for-age with others of the same age and gender. Standard growth charts for those 2 to 20 years old plot height and weight separately, resulting in two percentile rankings. Infants from birth to 36 months have a specific chart that compares length-for-age, weight-for-age and weight-for-length with babies of the same age and gender. The BMI growth chart compares a single body mass index score, which is calculated from a child's or teen's height and weight measurements. Doctors often use BMI rankings as measures of a child's or teen's body fat.

Things You'll Need

• Measuring tape
• Bathroom scale

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Instructions

Standard Growth Chart

• 1

  Weigh your child in pounds or kilograms on an accurate bathroom scale. If you have an infant, weigh yourself alone and then weigh yourself holding your baby. Subtract the smaller number from the larger number to get your baby's weight. Record the number.

• 2

  Measure your child's height, or stature, in inches or centimeters by having him stand barefoot with his back against a wall. Lightly mark the wall with a pencil at the crown of his head. If you have an infant, lay her down on a large sheet of paper or other surface that you can lightly mark. Make a pencil mark at the crown of her head and at the heel of one gently, fully extended leg. Use the measuring tape to get the child's height or the baby's length. Record the number.

• 3

  Locate the chart for your child's gender and age. Boys and girls of every age have separate charts. Each chart includes one area to mark the child's height-for-age and another to mark his weight-for-age. For babies, the three areas are length-for-age, weight-for-age and weight-for-length.

• 4

  Plot your child's weight on the portion of the chart labeled for weight by tracing your finger up from his age at the bottom of the chart to his weight listed on the side of the chart. The chart lists both kilograms and pounds, so ensure you plot for the unit of measurement you used when weighing your child.

• 5

  Plot your child's height on the portion of the chart labeled for height by tracing your finger from his age at the bottom of the chart to his height listed on the side of the chart. Both inches and centimeters are listed, so again, ensure that you plot for the unit of measurement you took.

• 6

  Interpret the chart. For example, if you have a 7-year-old son who is 51 inches tall and weighs 55 pounds, his height would be plotted between the 90th and 95th percentiles, while his weight would be plotted just above the 50th percentile. This means that for height, your son is as tall as or taller than 90 percent of boys his age, while 10 percent of boys his age are taller. For weight, 50 percent of boys his age weigh the same or less, while 50 percent weigh more.

BMI Percentile Chart

• 7

  Measure your child's height in inches and his weight in pounds. Record the figures.

• 8

  Calculate his BMI score by dividing his weight in pounds by his height in inches squared. Multiply the result by a conversion factor of 703. For example, if your son is 51 inches tall and weighs 55 pounds, using the calculation (55 / (51 x 51)) x 703, his BMI score would be 14.9.

• 9

  Use the BMI age-growth chart that corresponds to your child's gender to find his percentile. A 7-year-old boy with a BMI of 14.9 would be just above the 25th percentile for his age group.

• 10

  Interpret the BMI score. In this child's case, 25 percent of boys his age have the same or less body fat than he does, while 75 percent have more. BMI percentiles are further categorized: scoring below the 5th percentile is considered underweight, scoring between the 5th and 85th percentiles is considered a healthy weight, while scoring between the 85th and 95th percentiles is considered overweight. Scoring above the 95th percentile is categorized as obese.