📏 Height Calculator
Predict a child's adult height from the parents' heights using the mid-parental method, the rule of thumb paediatricians use. It gives a range rather than a number, because that is all the method honestly supports.
Predicting adult height, and the honest width of the answer
Height is strongly heritable, with twin studies putting around 80% of the variation down to genetics in well-nourished populations. That sounds like a prediction should be easy. It is not, because height is influenced by hundreds of genes plus nutrition, sleep, illness and hormones, so the parents explain most of it and not nearly all.
The mid-parental method
The rule paediatricians use is simple and roughly as good as the complicated alternatives:
boys: (father + mother) / 2 + 6.5 cm girls: (father + mother) / 2 − 6.5 cm
The 6.5 cm, about 2.5 inches, is half the average adult height difference between men and women. For a father of 178 cm and a mother of 165 cm, the mid-parental height is 171.5 cm, so a son is predicted at 178 cm and a daughter at 165 cm.
The range is the real output
The prediction carries a 95% range of roughly ±8.5 cm, which is a 17 cm spread. That is not the method being poor; it is the genuine variation. Siblings with identical parents routinely differ by ten centimetres, and a prediction that quoted a single number to the millimetre would be pretending to a precision nobody has.
| Father | Mother | Son | Daughter |
|---|---|---|---|
| 170 cm | 155 cm | 169 cm ±8.5 | 156 cm ±8.5 |
| 175 cm | 162 cm | 175 cm ±8.5 | 162 cm ±8.5 |
| 180 cm | 167 cm | 180 cm ±8.5 | 167 cm ±8.5 |
| 188 cm | 173 cm | 187 cm ±8.5 | 174 cm ±8.5 |
Better methods, and why they need a clinic
The Khamis-Roche method uses the child's current height and weight alongside the parents' heights and is more accurate, within about 5 cm. Bone age radiography, which compares the maturity of hand and wrist bones against standards, is better still, because it reveals how much growing is left rather than inferring it from age. Both need measurements this calculator does not have.
A rough shortcut sometimes quoted: a child's height at age two is about half their adult height for boys, and a girl's height at eighteen months is about half hers. It is less accurate than the mid-parental method but it needs no parental measurements.
Growth patterns worth knowing
Children do not grow steadily. Growth is fastest in infancy, settles to about 5 to 6 cm a year through childhood, then accelerates sharply at puberty: roughly 8 to 12 cm a year for girls around 11 to 13, and for boys around 13 to 15. Growth plates close about two years after puberty begins in girls and later in boys, which is why boys who seem short at 14 often catch up substantially.
A child tracking consistently along the same percentile curve is growing normally, whatever the percentile. What warrants attention is crossing percentile lines, in either direction, which is a growth-rate question rather than a height question.
What genuinely affects the outcome
Nutrition is the largest modifiable factor, which is why average heights in many countries rose dramatically through the twentieth century: Dutch men gained about 20 cm in 150 years, far faster than genetics could move. Adequate protein, sleep, and the absence of chronic illness all matter. Supplements, stretching and hanging from bars do not, once nutrition is adequate.
This page explains published formulas and population averages. It is general information, not medical advice, and it cannot account for your individual health.
If this is one step in a larger decision, the BMI calculator is usually the next question, and the ideal weight calculator is worth a look while you are here.
Frequently Asked Questions (FAQs)
How accurate is a height prediction?
The mid-parental method carries a 95% range of about ±8.5 cm, so the honest output is a 17 cm band. Khamis-Roche, which uses the child's current measurements too, narrows it to around ±5 cm. Bone age assessment at a clinic is the most accurate method available.
At what age do people stop growing?
Most girls reach adult height by 14 to 16 and most boys by 16 to 18, when the growth plates close. Late developers can add a little into the early twenties, but significant growth after 18 is unusual and almost always reflects a late puberty.
Can anything make a child taller?
Adequate nutrition, sleep and general health allow a child to reach their genetic potential; nothing reliably exceeds it. Growth hormone treatment exists for diagnosed deficiency and specific conditions, prescribed by an endocrinologist. Supplements and stretching do nothing.
Why are my children different heights with the same parents?
Because height is polygenic: hundreds of genes contribute, and siblings inherit different combinations. A ten-centimetre difference between siblings is entirely normal and is exactly why the prediction carries such a wide range.
Does the mid-parental method work for all populations?
The 6.5 cm sex adjustment is reasonably consistent, but the baseline varies between populations because average heights differ. The method works best when compared against growth charts for the child's own population rather than a universal standard.
When should I be concerned about a child's growth?
When they cross downward through percentile lines, grow less than about 4 cm a year in mid-childhood, or sit far outside the range predicted by their parents. The rate of growth matters more than the absolute height, and a paediatrician can assess it properly.