How tall will I be?
By inheriting genes from both parents, a child usually grows to their average height. However, the activity of genes can vary, and so too can growth. And beyond genes, there are environmental factors like wellness, activity, and nutrition. Height calculators can’t possibly take all of this into consideration to answer the question, “How tall will I be?” Instead they really only apply to statistical averages. Nevertheless, it can be interesting to try them out. The second calculator below takes more into account and tends to be more accurate.
The simplest height calculator (second one) draws on the fact that children inherit genes from both parents. It takes the average height of the parents and add 2.5 inches (6.5cm) for boys or subtract 2.5 inches for girls. But if the child’s height trajectory points to a greater height, don’t go hunting down the mailman just yet; with so many genes involved, some of which may be recessive, and the possibility of environmental influences, child height can differ considerably from parental height.
Another popular approach to predicting adult height is to double a boy’s height at age 2 or a girl’s height at age 18 months. While this approach does incorporate the child’s own height, and thus their own genetics, it is over simplified and unlikely to provide an accurate prediction.
The Khamis-Roche Method1 combines the best of both of these methods by looking at both parental height and the child’s height at the current age. Furthermore, it incorporates weight as this too is telling of growth to come. This is the method used by the first height calculator at the beginning of this article.
More advanced height calculators make use of bone age, which is a measure of age based on the size and shape of the bones as seen in radiographs, and formulas such as those found in the Tanner-Whitehouse method. Bone age isn’t always available, and it was actually for this reason that the Khamis-Roche method was developed.
Another method is to calculate height percentile and then check that same height percentile for adults. Similarly, there are also growth charts for analyzing height, but that’s a topic for another article.
While a height calculator may be useful, it is not intended for cases where an underlying height related disorder or syndrome may be present. Additionally, these methods have generally been developed for white American children and thus some prediction accuracy may be lost for other populations. In actuality, a pediatrician or endocrinologist is the best resource when it comes to understanding a child’s height.