Child Height Predictor – How Tall Will My Child Be
Estimates your child's adult height using three methods: mid-parental height, Khamis–Roche (ages 4–17), and the double-height-at-age-2 rule. Enter the parents' heights, the child's sex, age, height and weight to see the predictions.
Estimate Your Child's Adult Height
Height Predictor Formula
Where:
- \(M\) — mother's height (cm)
- \(F\) — father's height (cm)
- \(H_{\text{mid}}\) — mid-parental target height (cm)
- \(H\) — child's current standing height (cm)
- \(W\) — child's current weight (kg)
- \(a_0, a_1, a_2, a_3\) — age- and sex-specific coefficients of the Khamis–Roche method (valid for ages 4–17)
The first equation is the mid-parental (target height) rule: it estimates the genetic potential from the parents' heights alone, with a 13 cm adjustment for sex. The second is the Khamis–Roche equation, which refines the prediction by adding the child's own stature and weight to the parents' average height.
Height Predictor – Calculation Example
Example: a 6-year-old boy is 116 cm tall and weighs 20.5 kg; his mother is 164 cm and his father is 178 cm tall.
Mid-parental height:
\[ H_{\text{mid}} = \frac{164 + 178 + 13}{2} = \frac{355}{2} = 177.5 \text{ cm} \]
Khamis–Roche (coefficients for a 6-year-old boy: \(a_0 = -3.4\), \(a_1 = 0.50\), \(a_2 = 0.130\), \(a_3 = 0.70\)):
\[ H_{\text{adult}} = -3.4 + 0.50 \times 116 + 0.130 \times 20.5 + 0.70 \times 171 \approx 177.0 \text{ cm} \]
Result: both methods predict an adult height of about 177–177.5 cm (roughly 5 ft 10 in), with a realistic mid-parental range of about 169–186 cm. The doubling rule does not apply here because the boy is older than 2 years.
How to use the calculator
- Select the Height units — centimetres or feet and inches. All heights are entered in the units you choose.
- Enter the Mother's height and Father's height, measured without shoes.
- Select the Child's sex — boy or girl.
- Enter the Age in years (for example, 4.5 for 4 years and 6 months). The age is required for the Khamis–Roche method and the doubling rule.
- Enter the child's Current height, measured standing, without shoes.
- Enter the Current weight and pick its Unit (kg or lb). Weight is used only by the Khamis–Roche method.
The results appear in three blocks — one per method — followed by a comparison table and notes. If a method does not apply to your child's age, the calculator explains why.
How tall will my child be?
Adult height is largely genetic: studies suggest that roughly 60–80% of the variation between people is inherited from their parents. That is why the parents' heights alone give a useful first estimate. The mid-parental method averages the parents' heights and adds 13 cm for a boy (or subtracts 13 cm for a girl), producing the child's genetic target height. Most children — about 90% — end up within ±8.5 cm of this target, so the range matters as much as the single number.
The mid-parental method knows nothing about the child, however. Two siblings with the same parents can follow very different growth paths. The Khamis–Roche method improves on this by combining the child's own height and weight with the parents' average height through age- and sex-specific coefficients. It typically predicts adult height within about 2–3 cm before puberty, though during puberty the error can grow to 5–8 cm because children start and finish their growth spurt at different times.
A third, simpler rule of thumb: boys reach roughly half of their adult height by age 2, and girls by about 18 months. Doubling the height measured at that age gives a rough adult estimate. It is a folk guideline rather than a validated clinical method, but it often lands surprisingly close to the other two approaches.
The three methods at a glance
| Method | Uses | Best for | Typical accuracy |
|---|---|---|---|
| Mid-parental height | Parents' heights only | Any age, including toddlers | ±8.5 cm (90% range) |
| Khamis–Roche | Child's height, weight, parents' heights | Ages 4–17 | ≈ 2–8 cm |
| Double height at 2 (boys) / 18 months (girls) | One measurement at that age | A quick sanity check | Rough guideline only |
Assumptions, limitations and practical tips
- Measure standing, without shoes. A height taken lying down (the usual way for infants) runs about 0.7 cm longer than standing height.
- Interpret the range, not the single number. An 8–9 cm spread above and below the prediction is completely normal.
- Puberty timing shifts predictions. Early developers finish growing sooner and may already be close to their predicted height at 12–13; late developers can still grow well past 16.
- Special cases reduce accuracy. Very premature birth, chronic illness, malnutrition, or hormonal conditions can push a child off the genetic track predicted from the parents.
- One measurement is never a trend. A pediatrician plotting height on a growth chart over several years is far more informative than a one-time formula.
If your child's current height is far outside the mid-parental range, or if they are crossing percentiles up or down on a growth chart, bring the measurements to your pediatrician. To put today's result in context, you can also check your child's measurements against a child's height and weight chart, look at how fast they are growing with the infant growth velocity calculator, or follow their overall milestones with the child development tracker.
Frequently Asked Questions
How do I calculate my child's adult height by hand in inches?
If you work in inches, the sex adjustment is about 5 inches instead of 13 cm. Add the mother's and father's heights, add 5 inches for a boy (or subtract 5 inches for a girl), then divide by 2. Example: mom is 5 ft 4 in (64 in) and dad is 5 ft 10 in (70 in): (64 + 70 + 5) ÷ 2 = 69.5 in, or about 5 ft 9½ in for a son.
Which of the three methods is the most accurate?
From age 4, the Khamis–Roche method is usually the best: because it uses the child's own height and weight, it typically lands within about 2–3 cm before puberty. The mid-parental formula is a good fallback for toddlers and if you only know the parents' heights, but its 90% range is ±8.5 cm. The doubling rule is a quick sanity check, not a validated clinical method.
At what age is a height prediction most reliable?
Predictions are least certain in infancy and around puberty. In growingspurt years the timing of puberty varies so much that even Khamis–Roche can miss by 5–8 cm — a late developer at 13 may grow far beyond their prediction. From about age 4 until the first signs of puberty, and again once puberty is nearly over, estimates are the most dependable.
Can a doctor predict height more accurately with an X-ray?
Yes. A pediatrician can take an X-ray of the hand and wrist to determine the child's bone age, then combine it with height and parental height using methods such as Bayley–Pinneau or Roche–Wainer–Thissen. Because bone age shows how far the skeleton has matured, these methods handle early and late developers much better than formulas based on calendar age alone.
Why do the methods give different numbers for my child?
Disagreement is normal because the methods measure different things. Mid-parental height reflects only genetic potential and knows nothing about your child's build or pubertal timing; Khamis–Roche adds the child's actual measurements, so a tall-for-age child will get a higher result. If the estimates differ by more than about 8–10 cm, or your child is crossing percentiles, discuss it with your pediatrician.
Can nutrition, sleep, or sports change how tall my child will be?
Genetics set the ceiling, but environment decides how close a child gets to it. Chronic undernutrition, illness, or untreated hormonal conditions can cost several centimetres, and no supplement will push a well-nourished child past their genetic target. A balanced diet, adequate sleep, and regular physical activity support normal growth but do not dramatically exceed the prediction.
My child is under 2 — which method should I use?
Use the mid-parental method: it works at any age, including newborns, because it needs only the parents' heights. Khamis–Roche requires ages 4–17, and the doubling rule needs the measurement taken at about age 2 for boys or 18 months for girls. If your baby's length was measured lying down, subtract about 0.7 cm and record it for the doubling estimate later.