This tool estimates a child’s likely adult height from both parents’ heights using the well-established mid-parental height method used by paediatricians. It is a quick, evidence-based way to get a realistic expectation for how tall a child may grow, complete with the natural range around the estimate.
How it works
The method combines the two parents’ heights and adjusts for the child’s sex, because adult men are on average about 13 cm taller than adult women. For heights in centimetres:
Boy: (mother + father + 13) ÷ 2 Girl: (mother + father − 13) ÷ 2
The tool then shows a likely range of ±8.5 cm around the estimate, since roughly 95% of children fall within that band. Imperial heights are converted to centimetres first, and results can be displayed in either unit.
Example
A boy with a mother of 165 cm and a father of 178 cm:
(165 + 178 + 13) ÷ 2 = 356 ÷ 2 = 178 cm
So his predicted adult height is about 178 cm, with a likely range of roughly 169.5 cm to 186.5 cm. For a girl with the same parents, the estimate would be (165 + 178 − 13) ÷ 2 = 165 cm.
Why parental height predicts adult height
Height is strongly heritable. Studies consistently find that parental heights explain a large proportion of the variation in adult height across populations, making them the single most useful predictor available without a bone-age X-ray or genetic panel. The mid-parental height method formalises this intuition into a simple formula that clinicians have used for decades as a quick screening tool in paediatric growth assessments.
It is not the only predictor that matters, however. Actual adult height depends on:
- Nutrition during childhood and adolescence — chronic undernutrition can substantially reduce final height below genetic potential.
- Chronic illness — conditions that affect nutrient absorption, hormone levels, or bone growth can suppress height.
- Hormonal factors — growth hormone and thyroid hormone deficiencies, if untreated, cause short stature well below what parental heights would suggest.
- Birth order and family size — some research suggests later-born children in large families average slightly shorter, though the effect is small.
- Secular trend — average heights have increased in most countries over the 20th century due to improved nutrition, meaning a child may exceed the prediction derived from parents who grew up under different nutritional conditions.
When to use this — and when to see a doctor
This tool is appropriate for parents curious about a child’s likely adult size, for comparing a child’s growth trajectory with a reasonable genetic target, or for general family planning discussions. It is not a diagnostic tool.
A paediatrician will typically compare a child’s actual growth to the mid-parental height target as part of a growth assessment. If a child’s growth is consistently tracking well below the mid-parental target (or above it), or if growth velocity has slowed significantly, that warrants clinical evaluation — bone age X-rays and hormone tests can identify treatable causes of short stature. The ±8.5 cm range here reflects natural genetic variation, not a threshold for concern; falling anywhere within it is entirely normal.
This is a statistical guide, not a guarantee. Everything is calculated in your browser — nothing is uploaded.