When my kids were little, our friends used to predict that the bunch of them would tower over me once they reached adulthood. Speculating how tall our kids will be as adults, who they’ll marry or who they will most resemble is a popular guessing game. While some of the predictions rely on folklore, modern science has provided us with a couple of “height calculators” that can provide us with a reasonable figure of just how tall our kids will be as adults. Since my kids are fully grown, and I just so happen to have their growth charts at my fingertips, it’s easy for me to determine just how accurate these calculators really are.

Parent’s Height +/- 3
Many online sites use a variation of this simple calculator which bases its numbers on the point that children will grow up to reach a height somewhere between both their parent’s height. This calculator adds both parents heights together (in inches), divides this number by 2, and then either adds 3 inches if a boy or subtracts 3 inches if a girl.

The Khamis-Roche Method
This method uses both parents’ heights and the child’s current age, weight and height to come up with an estimate. This method is regarded as the most accurate and is projected to come within 1.5 inches of a child’s adult height. The Khamis-Roche calculator can be found at kidsgrowth.com.

So how did the calculators measure up when it came to my children? Both calculators projected that my two sons would probably grow to a height of 6ft 3.5 inches and that my daughter would probably be 5ft 10 inches or so. While one of my sons hit his predicted height, my other son ended up several inches shorter than his younger brother which irritates him to no end. As far as my daughter, she came in 2.5 inches shorter than both the calculators had estimated.

I’m not surprised at the discrepancy. After all, a variety of medical conditions, nutrition and genetics all play a role in how tall our kids grow. One look at my diminutive Scotch-Irish mother-in-law, and it’s easy to see why my daughter isn’t as tall as I am. The same goes for my oldest son who, instead of inheriting his father’s tall slender frame, ended up built like his 5’10” Dutch grandfather.

When it comes to predicting a child’s height as an adult, kids-height calculators seem to be as accurate as the folk wisdom our grandmothers relied on back when our parents were children. According to Grams, a child’s adult height can be calculated by measuring at child’s height at age 2, and then doubling the number.

Interestingly enough, this folksy formula was the most accurate in predicting my children’s adult height. At age 2, all three of my children were almost exactly half the height they are as adults, which suggests that folk wisdom can on occasion outwit science.