Kids Growth Chart Percentiles Calculator

Reading a Growth Chart

An example of how to use and read a growth chart.
An example of how to use and read a growth chart to calcuate your child's percentiles. Vincent Iannelli, MD

A growth chart is an important tool for pediatricians to monitor your child's growth.

Growth Chart Percentiles

Instead of simply wanting to know if their child is growing well and following a growth curve, most parents want to know where they are on the growth curve.

Are they at the top, bottom, or in the middle?

Online growth charts available online make it so that you don't even have to wait until your next check up to see how your child is growing.

Do you know how to calculate your child's percentiles for height and weight from a growth chart?

Reading Growth Charts

This guide and the included photo should provide you with all of the information you need to use growth charts and follow how well your child is growing.

The first step is to find the right growth chart. In this example, we are going to find the percentile for a 2-year-old boy who weighs 30 pounds, so we will use the growth chart for Boys from Birth to 36 Months.

Next, (step A on the example growth chart) find the child's age at the bottom of the chart and draw a vertical line on the growth chart*. In this example, we drew a line through 24 months (2 years).

Now find the child's weight on the right-hand side of the chart, 30 pounds in this example, and draw a horizontal line*. This is step B in the example.

*You don't have to physically draw a line on the growth charts. If you really do that each time, your growth chart will become messy and hard to read over time. Instead, just imagine where the line should be, or draw a light line with a pencil that you can later erase.

Step C involves finding the spot where these two lines intersect or cross each other. 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 (step D).

In this example, you can see that a 2-year-old boy who is 30 pounds is at the 75th percentile for his weight.

What does that mean? It means that he weighs more than about 75% of boys his age. It also means that 25% of 2-year-old boys weigh more than he does. Is that normal? Sure, if that is where he has always been on the growth charts.

Finding your child's percentile is a little harder if the curve doesn't actually pass through the spot where your child's age and weight come together. For example, what would you do if the boy in our example actually weighed 31 pounds? You would use all of the same steps and 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 also not be able to find an exact percentile, except to say that he is above or below the growth chart.

You can use the same steps to plot your child's height and body mass index.

Here are some more examples (try them before looking at the answers below):

  1. What is the percentile for a 2-year-old boy who is 2 feet 10 1/2 inches (34 1/2 inches)?
  1. What is the percentile for a 13-year-old girl who is 80 pounds?
  2. What is the percentile for a 16-year-old girl who is 5 foot 4 inches (64 inches)?
  3. What is the percentile for a 9-year-old who has a body mass index of 18?
  4. What is the percentile for a 6-month-old girl who is 14 pounds?

What Do Percentiles Mean?

It is important to understand that the 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 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% of kids his age weigh more than he does), if he has always been at the 5th 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 5th 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.

Answers to examples: 1) 50th percentile, 2) 10th percentile, 3) 50th percentile, 4) 75th percentile, 5) about the 15th percentile

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