Which Child Height Prediction Method Is Most Accurate?
Bone-age X-ray, Khamis-Roche, and mid-parental height compared honestly — accuracy, what each one needs, and when each makes sense.
This article explains height-prediction methods for educational purposes and is not medical advice. If you have concerns about your child’s growth, consult a pediatrician.
Ranked by accuracy: bone-age X-ray (most accurate, needs a doctor) beats the Khamis-Roche method (about ±2 inches, needs the child’s current height, weight, and age), which beats the mid-parental formula (±8.5 cm, needs only the parents’ heights).
Every height predictor — online or in a clinic — is built on one of these three methods. The honest difference between them is not magic, but data: how much information about the child they use, and how wide the margin of error is.
Below: how each method works, its real accuracy, and a clear rule for which one fits your situation.
The three methods at a glance
Here is the short version, before we go deeper into each one:
| Method | Typical error | What you need | Cost / access |
|---|---|---|---|
| Bone-age X-ray | Most accurate | Doctor visit + hand X-ray | Clinic only |
| Khamis-Roche | ±~2 inches (~5 cm) | Child’s age, height, weight + both parents’ heights | Free calculator |
| Mid-parental | ±8.5 cm (~3.3 in) | Both parents’ heights only | Free calculator |
Error margins are approximate published values. Individual results vary — growth is statistical, not exact.
Mid-parental height: the simplest estimate
This is the formula behind almost every free online predictor, and the one pediatricians quote in seconds:
- • Boys: (father’s height + mother’s height + 13 cm) ÷ 2
- • Girls: (father’s height + mother’s height − 13 cm) ÷ 2
Khamis-Roche: the most accurate formula
Published by Khamis and Roche in 1994, this method adds the child’s own current measurements — age, height, and weight — to the parents’ heights, using regression coefficients derived from a large longitudinal study. Because it uses where the child actually is right now, it consistently outperforms mid-parental height.
Its published error margin is roughly ±2 inches (about 5 cm) — noticeably tighter than mid-parental’s ±8.5 cm. It works for children roughly between ages 4 and 17, and the prediction gets better as the child gets older.
Bone age: the clinical gold standard
When a pediatrician really needs precision — for example, when a child’s growth curve looks unusual — they order a bone-age X-ray of the left hand and wrist. A specialist compares the image to reference standards (the Greulich-Pyle atlas being the classic one) to determine skeletal age, then combines it with the growth chart to forecast adult height.
This is the most accurate method available because it measures the child’s actual biological maturity, not just their calendar age. But it requires a doctor’s visit, radiation exposure (a very small dose), and clinical interpretation — it is not a DIY option.
For everyday curiosity, the formulas above are more than enough. And if you want a quick estimate right now, the free predictor on this site uses the mid-parental method:
Frequently asked questions
How accurate are online child height predictors?
Most free predictors use the mid-parental formula, so their honest accuracy is about ±8.5 cm (±3.3 inches) around the result. Treat the number as the center of a range, not a promise.
What is the Khamis-Roche method?
A height-prediction formula published in 1994 that uses the child’s age, height, and weight together with both parents’ heights. It is more accurate than mid-parental height — roughly ±2 inches — and works for children aged about 4 to 17.
Can doctors predict how tall my child will be?
Yes. Pediatricians combine the mid-parental estimate with the child’s growth curve, and when needed, a bone-age X-ray of the hand and wrist. Bone age is the most accurate clinical method because it measures skeletal maturity directly.
Which method should I use for a 3-year-old?
Mid-parental height is the reasonable choice — the Khamis-Roche method is validated from about age 4 onward. At 3, predictions are the least reliable anyway, since so much growth (and puberty timing) lies ahead.