Parents’ heights
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The clinic formula is mid-parental height
Average the two parents’ heights, then add 6.5 cm for a boy or subtract 6.5 cm for a girl. The adjustment is half of the roughly 13 cm average difference between adult men and women. That figure is the centre of the prediction, not the prediction itself.
A single number would be misleading
The error on this formula is wide: about 68% of children land within 8.5 cm of the mid-parental height, and 95% within 17 cm. Quoting one number turns it into a target, which is exactly the wrong thing to hand a parent. This page shows both bands.
Genetics is most of it, not all of it
Roughly 80% of the variation in adult height is heritable; the rest comes down to nutrition, sleep and chronic illness. Note also that this calculation does not look at the child at all — if you are worried about where they sit against their peers, that is a growth chart question for a paediatrician, not a formula.
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Frequently asked questions
QHow is a child’s adult height predicted?
By the mid-parental height method used in paediatric clinics. Average the parents’ heights, then add 6.5 cm for a boy or subtract 6.5 cm for a girl — half of the roughly 13 cm average difference between adult men and women.
QHow accurate is it?
Not very, and that is the point of showing ranges. About 68% of children finish within 8.5 cm of the figure and 95% within 17 cm. Treat the middle number as a centre of gravity, not a forecast.
QCan a child end up much taller than both parents?
Yes. Heritability accounts for roughly 80% of adult height variation, leaving real room for nutrition, sleep, illness and plain chance. That is why the 95% band is 34 cm wide.
QWhat about feet and inches?
Enter heights in centimetres — one inch is 2.54 cm, so 5 ft 9 in is 175.3 cm. The formula itself is unit-free; only the 6.5 cm adjustment is metric, and it equals about 2.6 inches.
QDoes the child’s current height improve the estimate?
Not here. This calculation uses only the parents. The current height you enter is shown as a distance from the predicted centre, nothing more. Tracking growth over time is what a paediatric growth chart is for.