How to Measure Baby Length for a Growth Chart

By Rosenya Faith
A close-up of a pediatrician measuring an infant.
A close-up of a pediatrician measuring an infant.

Your infant grows at a rapid rate, tripling his birth weight in his first year and growing approximately 10 inches, or 50 percent in length. Your health care provider measures his weight and length at every checkup to determine whether your baby is developing proportionately. If his weight or height is increasing more rapidly than normal, he might be feeding too often. No increase in weight or sluggish gains may indicate an inadequate supply of calories, which may be a result of a variety of underlying issues.

Taking Measurements

Your baby is weighed on a special infant scale that has a large enough tray to cradle your infant's head and body and can measure up to 20 kg in 0.01 kg or 1/2 ounce increments. Your health care provider removes your infant's clothing and diaper to obtain an accurate measurement of weight.

While special lengthboards can be used to accurately measure infant length, often your health practitioner measures your infant in the recumbent position -- lying down -- on an examination table with a soft measuring tape. Your health care provider measures from the top of your infant's head, presses down gently to extend his legs and measures to the bottom of the heels of his feet.

Growth Charts

Infant growth charts are a means of ensuring your infant is growing at a steady rate, and the percentiles recorded on the chart are a way of comparing the growth rates of infants of the same age and gender. Percentile statistics are compiled from thousands of measurements, obtained from infants throughout the United States. Because babies come in all shapes and sizes, there is no single ideal number for your infant. A baby in the 10 percentile may be just as healthy as a baby in the 50th or 90th percentile. A healthy child generally stays within a particular percentile on the growth chart throughout the year.

Understanding Percentiles

The percentiles are drawn as curved lines on a growth chart. A high percentile suggests that an infant is larger than most infants of the same age and gender. A low percentile suggests that an infant is smaller than most babies of the same age and gender.

When your health care provider says that your infant is in the 90th percentile of an infant weight chart, this means that 90 percent of infants of the same age and gender weigh less and just 10 percent weigh more than your baby. An infant in the 50th percentile weighs less than 50 percent of infants of the same age and gender, and more than the remaining 50 percent.

Beyond Averages

While the percentile statistic allows your health practitioner to track your baby's growth against the average, what is more important is your infant's individual change in growth between each visit.

If an infant begins in the 10th percentile, and remains within the same percentile throughout his first year, this suggests a healthy pattern of growth, particularly if his parents and siblings are of small stature as well.

However, if an infant begins in the 30th percentile and later measures in the 10 percentile, this may suggest a failure to thrive -- a failure to gain weight or grow as expected.

About the Author

Rosenya Faith has been working with children since the age of 16 as a swimming instructor and dance instructor. For more than 14 years she has worked as a recreation and skill development leader, an early childhood educator and a teaching assistant, working in elementary schools and with special needs children between 4 and 11 years of age.