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Understanding Growth Charts

Instructions for using growth charts

Growth charts are an important way for pediatricians to monitor your child's growth. With the availability of growth charts on the Internet, many parents have begun using them at home too.

Since the growth charts compact a lot of information into a small space, they can be a little confusing to use and I often get requests for help from parents who don't understand how to plot their child on the charts.

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

The first step is to find the right growth chart. In our 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 chart below) find your child's age at the bottom of the chart and draw a vertical line (a straight line up and down) on the growth chart. In our example, we drew a line through 24 months or 2 years.

Now find your child's weight on the right hand side of the chart, 30 pounds in our example, and draw a horizontal line (a straight line from side to side). This is step B in our example. Keep in mind that you don't have to really physically draw a line on the growth charts. If you really do that each time, your growth chart will look very messy and will be hard to read. 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 our example, you can see that a two 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.

Growth Chart Examples

Finding your child's percentile is a little harder if a 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 would have to imagine a curve that is somewhere between the 75th and 90th percentiles and figure that he was at about the 80th-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)?
  2. What is the percentile for a 13 year old girl who is 80 pounds?
  3. What is the percentile for a 16 year old girl who is 5 foot 4 inches (64 inches)?
  4. What is the percentile for a 9 year old who has a body mass index of 18?
  5. What is the percentile for a 6 month old girl who is 14 pounds?

It is also 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 where he is at any one time. Even if your child is at the 5th percentile for his weight, which means 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: A) 50th percentile, B) 10th percentile, C) 50th percentile, D) 75th percentile, E) about the 15th percentile

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