Height Distribution Simulator centimetres

Nobody inherits a height — they inherit the parameters of a distribution. Enter the heights of whichever relatives you know. The predicted child isn't a single number but a curve, and that curve gets narrower the more of the family you fill in. Calibrated on Galton's real data (h²≈0.72); grandparents & siblings added via quantitative-genetics relatedness.

The family

Grandparents
Parents
Existing children (siblings of the predicted child)
Enter each sibling's height and age. Age ≥ 18 = grown (final height); younger = measured against age peers and discounted by how strongly height tracks at that age.
Predict for
Child's measured growth (optional)
Each = a paediatric growth-chart percentile (WHO/CDC) at a given age. Height tracks, so a percentile at 12 pins the adult far tighter than at 2. Add several — overlapping ages are correctly de-duplicated, not double-counted.
Birth cohort (secular trend)
Each person is judged relative to their own generation; the child's inherited rank is then expressed in their cohort.
Model & display
0.72

Predicted child height

Child's generation average (no family info) Predicted — boy Predicted — girl shaded band = 80% range (10th–90th percentile)

How it works. Every person is a draw from a Normal. In sex-standardised z-space the phenotypic correlation between two relatives is (genetic relatedness) × h² — 0.5 for parent–child and full siblings, 0.25 for grandparent–grandchild. The child's curve is the conditional Normal given the relatives you entered (Gaussian conditioning on the additive-relatedness covariance matrix). Known relatives pull the mean toward them and shrink the variance. Heritability is estimated from Galton's 898 parent–child records (h²≈0.72); the grandparent layer is theory-derived because no open 3-generation human height dataset exists (Framingham requires an IRB/dbGaP application).
Cohort means are real per-country trajectories by year of birth from NCD-RisC (eLife 2016, "A century of trends in adult human height"), covering birth years 1900–1995. Growth measurements are folded in as a joint multivariate-normal of childhood-to-adult tracking correlations, so overlapping ages don't double-count.