What this calculator does
Height is strongly heritable, and the mid-parental method uses that: average the two parents, then add or subtract 6.5 cm depending on the child's sex. It is the standard first estimate in paediatric growth assessment.
The prediction carries a wide range. A 165 cm mother and 178 cm father give a predicted 178.0 cm for a boy, but the likely range runs from 168.0 to 188.0 cm, a full 20 cm spread that reflects how much individual variation remains.
The formula
Add both parents' heights, add 13 cm for a boy or subtract 13 cm for a girl, then halve. The conventional range is 10 cm either side of the result.
| Term | Meaning |
|---|---|
| Mid-parental height | The predicted adult height from both parents. |
| Target range | Roughly 10 cm either side, within which most children fall. |
| Tanner method | The 1970 convention this calculator applies. |
The inputs explained
| Field | What to enter |
|---|---|
| Mother’s height (cm) | The mother's height in centimetres. |
| Father’s height (cm) | The father's height in centimetres. |
| Child’s sex | The child's sex, which sets whether 13 cm is added or subtracted. |
When to use it
Assessing a child's growth
Paediatricians compare a child's growth curve against the mid-parental target range.
Putting a growth chart in context
A child tracking below average may be exactly where their genetics predict.
Understanding a referral
Growth well outside the target range is one of the triggers for further assessment.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How do parent heights combine?
Three parent height combinations.
| Mother's height (father 178 cm) | Predicted adult height | Likely range (± 10 cm) |
|---|---|---|
| 160 cm | 175.5 cm | 165.5 – 185.5 cm |
| 165 cm | 178.0 cm | 168.0 – 188.0 cm |
| 172 cm | 181.5 cm | 171.5 – 191.5 cm |
Questions
How accurate is the prediction?
It captures the genetic average but not the individual. The 10 cm range either side exists precisely because roughly a third of children fall outside a much narrower band, and some fall outside the full range.
Why 13 cm?
It approximates the average adult height difference between men and women in the populations the method was developed on. That gap differs somewhat between populations, which is one source of error.
What if a child is growing outside the range?
It is worth raising with a paediatrician, though it is not automatically a problem. Growth depends on nutrition, health, timing of puberty and much else besides parental height.
Are there better methods?
Yes for specific purposes. Bone age assessment from a hand X-ray predicts more accurately, particularly around puberty, but it requires imaging where this requires two numbers.
For weight-for-height in adults, see the BMI calculator. For a reference weight from height, see the ideal weight calculator.