Height Calculator: Predicting How Tall a Child Will Be

The method is called mid-parental height, and paediatricians use it as a rough check rather than a forecast. The margin around it is wide enough that the margin is really the story.

The mid-parent method, worked through

In centimetres: add both parents' heights, add 13cm for a boy or subtract 13cm for a girl, then divide by two. In feet and inches the adjustment is 5 inches instead of 13cm. That is the whole formula.

One family, two children

Father 180cm (5ft 11in), mother 165cm (5ft 5in).

For a son: 180 + 165 + 13 = 358, halved is 179cm, or 5ft 10.5in. For a daughter: 180 + 165 - 13 = 332, halved is 166cm, or 5ft 5.5in.

Now the part a single number hides. The accepted margin around a mid-parental estimate is about 8.5cm either side. The son's realistic bracket is 170.5 to 187.5cm, which is 5ft 7in to 6ft 2in. That is a 17cm span, close to seven inches. The estimate is the centre of a wide band, not a prediction.

How to use the height calculator

Enter the mother's height, the father's height and the child's sex. Switch the unit toggle if you think in centimetres rather than feet and inches. Better versions also take the child's current age and height and compare that against growth percentiles, which is a stronger signal than parental heights alone once a child is past about four.

Measure the parents rather than trusting memory. Self-reported heights run optimistic, and adults genuinely lose height with age. Shoes off, heels and shoulders against a wall, something flat across the top of the head. If you are converting a figure you already have, note that 5ft 9in is 175.3cm rather than 175, and a rounded centimetre to inch conversion can shift the final estimate by half an inch.

Why the band is so wide

Height is polygenic. Hundreds of variants each contribute a small amount, so a child can land well outside the average of two parents without anything unusual having happened. Tall parents can produce a child at the shorter end of the family and the arithmetic will still have been correct.

What moves a child off the family line

Nutrition through childhood and adolescence, sleep, chronic illness and the timing of puberty all shift the outcome. Timing in particular confuses parents. A boy who starts puberty late is often the shortest in his year at 14 and among the taller ones at 18, because his growth plates stay open longer. The reverse happens too, and an early growth spurt is not a promise of extra height at the end.

Growth plates close roughly two years after a girl's first period, and somewhere between 16 and 18 for most boys. That is the point where prediction stops being prediction and becomes measurement.

Common questions

How accurate is the mid-parental height formula? It puts most children inside its band, and the band is nearly seven inches wide, so accuracy is not really the right question. Treat it as a sanity check. If a child's growth curve is tracking far below the predicted range, that is the useful signal, and it is a reason to see a doctor rather than to recalculate.

Can you predict adult height from a child's current height? Approximately. One rough rule doubles a boy's height at age two, or a girl's at 18 months. In the example family above, a boy measuring 88cm at two projects to 176cm, sitting close to the 179cm mid-parental figure. Agreement between two crude methods is mildly reassuring, not proof of anything.

Do boys keep growing after 18? A small amount for some, usually under an inch, and mostly among those who entered puberty late. Once the growth plates fuse, the long bones are finished. What does keep changing is posture and spinal compression, which is why almost everyone measures a centimetre shorter in the evening than they did that morning.

Does a taller child need a higher healthy weight? Yes, and it scales with height squared rather than with height itself, which is why weight ranges climb faster than parents expect between one school year and the next. A child BMI calculator handles the age and sex adjustment that adult formulas skip entirely.