We live in an age where kids are measured from the moment they are born, right through school and through their adulthood. For parents, one of the things they are most curious about is how tall they’ll be as adults. A recent study tried to answer that question and, it turns out an old wive’s tale is as good a predictor as anything science can come up with.

Researchers have been trying to estimate how tall children will be as adults for some time. Studies back to the 1920s looked at heights of children and tracked them into adulthood. But those studies have typically only looked at very small sample sizes of perhaps just 200 or 300 subjects.

Nevertheless, there have been many studies done with small sample sizes and, collectively, they reveal some insights.

A number of these studies have been reviewed by researchers in a paper titled A chart to predict adult height from a child’s current height where statistical probabilities are applied to the aggregate of a bunch of studies. The start by saying parent height is often predicted by looking a other height of parents which makes some sense. But looking at a child’s current height is a far better predictor.

When my kids were little, the rule of thumb I was given was that you could take a child’s height at age two and double it to get a good estimate of adult height.

The study found that birth length is a fairly weak predictor but a child’s height at age four is a stronger metric for making that estimate. For example, if your four year old is about 107cm tall. -which puts them in the 90th percentile for height, there’ a good chance they’ll land at a height of about 183cm – the old six foot mark.

They also note in the study that heights during puberty aren’t a great indicator as growth spurts driven by hormonal changes throw the data into some disarray.

Going back to the ‘double the height at two’ rule – it turns out that’s as good a tool as any complex statistical analysis. The correlation between your toddler’s height and their predicted adult height is pretty solid, making it as good a predictor as a complex study of things like skeletal age and a bunch of other metrics.