How an adult height calculator actually works

The two methods behind every serious calculator

1. Mid-parental target height. Average the biological parents' heights with a sex adjustment — add 13 cm for boys, subtract 13 cm for girls — then divide by two. The result is a genetic target; most children land within about ±8.5 cm of it.

2. Khamis-Roche. A validated model, published in Pediatrics in 1994, that combines the child's age, sex, current height and weight with parental heights. It predicts adult stature without a bone-age X-ray and generally yields a somewhat tighter range when the inputs are available.

GrowTall implements both and shows each result on a visual scale — for example 165–178 cm — with the target marker in context. Details: Khamis-Roche · mid-parental height.

What you will need

• The biological parents' heights (in cm or ft-in) — required for both methods.
• The child's age, sex and a current height measurement — required for Khamis-Roche.
• Optionally a current weight — Khamis-Roche uses it as an input.

Reading the output like a pro

Treat every calculator's output the same way: as a corridor. If two methods overlap — say mid-parental 166.5–175.5 cm and Khamis-Roche 163–180 cm — the overlap region is the most informative part. Estimates naturally become more stable as a child moves through middle childhood and puberty, because more of the outcome has already happened.

Remember: a calculator estimates a range for a healthy child. It cannot diagnose a growth disorder, and it is not a substitute for pediatric evaluation.

Limits of any adult height calculator

• It cannot see the future — puberty timing alone can move the outcome by a couple of centimeters either way.
• It assumes generally good health; chronic conditions can change growth independently of the model.
• It is derived from population data, so individuals can fall outside the range.
• It stops meaning anything once growth plates close — adult height is, by then, simply measured.