THE THREE EASY STEPS TO CALCULATE HOW TALL YOUR CHILD WILL BE

THE THREE EASY STEPS TO CALCULATE HOW TALL YOUR CHILD WILL BE

In a society full of supermodels and athletic superstars, every parent wants to know how tall their child is going to be. It’s not nearly as mystical or complicated as one might think. There is a simple scientific formula used to calculate a child’s genetic growth potential.

What is “genetic growth potential?”

A child’s genetic growth potential simply means that if you take into account both parents, what is the child’s likelihood of growing to a certain size. It’s quite intuitive. Short parents have short kids. Tall parents have tall kids. If a child is significantly above or below his/her genetic potential, it can signify a problem.

How do I calculate my child’s growth potential? (How tall is my kid going to be?)

  1. Get mom’s height (in centimeters)
  2. Get dad’s height (in centimeters)
  3. Plug it into the simple formula (the trick is converting inches to cm).

FOR BOYS

[Mom’s height  + Dad’s height + 13 cm] divided by 2= potential height in cm

FOR GIRLS

[Mom’s height  + Dad’s height – 13 cm] divided by 2= potential height in cm

Help with the math

The next question is how to convert to centimeters.  It’s simple: Get the total inches and multiple by 2.54 cm (1 inch = 2.54 cm).

EXAMPLES:

  1. Let’s take me, for example. I am 5′ 9″. That is a total of 69″ (5 feet x 12 inches=60 inches, then add the extra 9 inches). Now pull out your calculator: 69 (my total inches) x 2.54 (the conversion factor) = 175.26 cm. I am 175.26 cm tall.
  2. Let’s take my husband, who is 6′ 6.5″. (6′ x 12″ =72″. Then add 6.5″ for a total of 78.5″). 78.5 (total inches) x 2.54 (to convert to cm) is 199.39 cm.
  3. Now put it together in the formula:

My son’s growth potential is calculated like this:

175.26 cm (mom’s height) + 199.39 cm (dad’s height) + 13  = 387.65 cm. Now divide that by 2 and the answer is 193.8 cm growth potential

Great, I figured that my son’s growth potential is 193.8 cm (but since I’m American, I want inches. So work backwards. 193.8 divided by 2.54 (reverse the conversion factor) = 76.3 inches (or 6′ 4.3″) is my son’s growth potential.

My daughter’s growth potential is:

175.26 cm (mom’s height) + 199.39 cm (dad’s height) – 13 = 361.65 cm. Now divide that by 2 = 180.8 cm growth potential (divided by 2.54 to get in inches = 71 inches or 5′ 11″)

Change it up: If I had married someone my same size, swap out 175 cm for the 199 cm in the equations.

Answer: My son’s growth potential would change to 5′ 11″ (not 6′ 4″) and my daughter’s would be 5′ 6″ (not 5′ 11″). So you can see the big difference one parent’s height can mean to a child’s ultimate growth potential.

What if my infant is much bigger/smaller on the growth curves?

It isn’t all that uncommon that I will have an infant that doesn’t match up with the calculated growth potential on the measured growth curves (especially in the beginning). For example, mom is 5′ and dad is 5′ 4″. They have an infant that measures 90% for height and weight. Instinctively, you know that this child should be smaller than average. The key is to remember that how an infant starts out doesn’t always reflect how a child will end long term. The early infancy usually reflects more about the health and growth environment in utero. In this example, the big infant may just be reflecting a perfectly healthy in utero growth and medically we would expect this child to drop into his/her much smaller genetic potential over the first few years of life.

Conversely, a set of tall parents may have a small infant who experienced stress/problems in utero (perhaps delivering premature). When the child is given a hardier growth environment out of the womb, he or she may make big gains in growth and “catch up” to his or her genetic potential.

What if my child is not meeting his or her genetic potential?

If you have just calculated your child’s genetic potential and it is way off (too big or too small), it may indicate a problem. With that said, there are plenty of variations within the same family (e.g., same-gender siblings are not always the same height). If your child is vastly off the expected norm, however, you should discuss it with your pediatrician. A pediatrician is well versed in normal growth patterns and can help you navigate whether the variation is something to worry about.

How can I ensure my child meets his/her growth potential?

While there are no guarantees, there are certainly things you can do to improve your child’s chances.

  1. Ensure a balanced, proper diet. Even with the tallest parents in the world, a malnourished child won’t grow well.
  2. Get good sleep. Getting enough, good sleep is an important part of the healing and restorative processes the body goes through on a daily basis. In order to grow, kids need good sleep.

Other tricks docs use to track growth

While the calculation is a well-accepted scientific calculation, doc’s always have other tricks up their sleeves.

  1. X-rays: X-rays that look at bones can calculate something called a bone age. It can give a doctor a lot of insight into how a child is growing if the bone age lines up with the chronological age (i.e., your bones look their real age). X-rays also look at growth plates at the ends of the bones. While an adult who is done growing has “closed” or “fused” plates, a child with growth potential will have lots of space in those growth plates.
  2. Tanner staging: When doing a physical exam around those puberty/adolescent years, a doctor can tell a fair amount about development and further growth potential depending on how developed a child is in puberty (specifically looking at genitals and chest/breast development).

As you go in for regular well-visits with your pediatrician, he or she should review with you how your child is growing. Don’t be bashful about bringing up any concerns you may have about  your child’s growth.

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About The Author

Dr. Monica Wonnacott

I'm a pediatrician and a mom. I've been doing this doctor thing for 10 years, and love it. I'm known for giving parents the straight scoop without always sugar-coating it. And I believe in educating parents. The more you know, the better care you give your kids.

Dr. Monica Wonnacott


I'm a pediatrician and a mom. PediatricAnswers.com is my blog where parents can get the straight scoop on their child's health, largely based on my experience in the office and at home. I don't diagnose on the site, so please don't ask. These are just my opinions. Use this site as a resource. And trust your parent gut.

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