How This Calculator Works
Use the four tabs above depending on what you're trying to find out. Child Height Predictor uses the Khamis-Roche method — a child's own age, current height, and weight, combined with both parents' heights — to estimate adult height for children roughly age 4 and up. Parents-Only Estimate is the simpler mid-parental formula, useful before a current height and weight reading exists, such as during pregnancy or in a baby's first year. Adult Height Percentile takes an adult's own height and shows exactly how it compares to the wider US population of the same sex, based on CDC measurement data. Height Converter is a straightforward two-way tool for switching between feet-and-inches, centimeters, meters, and total inches, with the fields updating each other live as you type.
The Khamis-Roche Method
The Khamis-Roche method is the most accurate widely-available height prediction that doesn't require an X-ray. Developed by Dr. Harry Khamis and Dr. Alex Roche and published in Pediatrics in 1994 (with a small correction issued in 1995), it's built on data from the Fels Longitudinal Study — a research project that tracked the growth of hundreds of children from birth into adulthood over several decades.
Rather than relying on parents' heights alone, it combines four pieces of information: the child's current age, current height, current weight, and the average of both parents' heights. Each of these is weighted differently depending on the child's age and sex, using a set of statistically-fit coefficients that shift smoothly across childhood — younger children's predictions lean more heavily on parental height (since a 5-year-old's own height doesn't yet say much about their adult stature), while older children's predictions lean more on their own current measurements, since by the mid-teens a child's own growth trajectory carries more information than genetics-only estimates.
The method is validated for children roughly age 4 through 17.5, and its published accuracy is tighter than the mid-parental formula alone: predictions typically land within about ±2.2 inches (5.6 cm) for boys and ±1.7 inches (4.3 cm) for girls of the eventual adult height. This calculator implements the published, peer-reviewed Khamis-Roche coefficients directly (Khamis HJ, Roche AF, "Predicting adult stature without using skeletal age: the Khamis-Roche method," Pediatrics 1994;94(4):504-507, erratum 1995;95:457) — every result is computed in your browser from the same statistical model, not looked up from a simplified table.
The Parents-Only (Mid-Parental) Formula
Khamis-Roche needs a current height and weight reading, which simply doesn't exist yet for an unborn baby or a newborn. For that situation, the Parents-Only tab uses the older, simpler mid-parental method — sometimes called the Tanner method after the researcher who formalized it — which starts by averaging both parents' heights, then adjusts for the roughly 13 cm (5 inch) average height gap between adult men and women:
- Predicted son's height = (father's height + mother's height + 13 cm) ÷ 2
- Predicted daughter's height = (father's height + mother's height − 13 cm) ÷ 2
For example, a father at 5'10" (178 cm) and a mother at 5'5" (165 cm) average out to 171.5 cm. Adding half of 13 cm (6.5 cm) predicts a son at about 178 cm (5'10"), while subtracting the same 6.5 cm predicts a daughter at about 165 cm (5'5"). Once a child is old enough to have a current height and weight of their own, switching to the Child Height Predictor tab will generally give a tighter, more individualized estimate.
Understanding Your Child's Predicted Range
Every prediction here is really the center of a range, not a guarantee. For the Parents-Only formula, about two-thirds of children end up within roughly ±8.5 cm (3.3 inches) of the mid-parental prediction, and about 95% end up within roughly ±17 cm (6.7 inches). For the Khamis-Roche method, the tighter published range is about ±2.2 inches (5.6 cm) for boys and ±1.7 inches (4.3 cm) for girls, since it has more information to work with. Genetics is estimated to account for somewhere between 60% and 80% of adult height overall, with the remainder shaped by nutrition, overall health, sleep, and other environmental factors during growth.
One subtlety worth knowing: statisticians have long noted that mid-parental height slightly overpredicts for very tall parents and underpredicts for very short parents, an effect called regression to the mean. In plain terms, an unusually tall couple's child tends to land a bit closer to average than the raw formula suggests, and the reverse is true for an unusually short couple. Both calculators here use the standard published formulas as-is, since the adjustment is small for most parent-height combinations, but it's worth keeping in mind if both parents sit at the extreme ends of the height range.
Khamis-Roche vs. Other Prediction Methods
Khamis-Roche is one of several ways to estimate a child's adult height, and it's worth understanding where it fits among the alternatives:
- Bone-age (skeletal maturity) methods use an X-ray of a child's hand and wrist, comparing bone development to reference atlases. These are generally the single most accurate predictions available, but they require a clinical visit and imaging that most families only pursue if a doctor has a specific reason for concern.
- Mid-parental height uses only the parents' heights, with no current-measurement requirement — the right tool before a child has a height and weight of their own to work with, but the widest error margin of the methods listed here.
- Growth-chart percentile tracking assumes a child continues along whatever percentile curve they're already following on a standard CDC or WHO growth chart. It's the method pediatricians lean on most during routine well-child visits, since it updates continuously as new measurements come in, and it doesn't require parental heights at all.
For a family who already knows both parents' heights and has a recent height/weight reading for a child age 4 or older, Khamis-Roche is the most accurate estimate available without a doctor's visit.
How Height Percentiles Work
The Adult Height Percentile tab compares a given height to the distribution of US adult heights measured by the CDC's National Health and Nutrition Examination Survey (NHANES, 2021–2023 data): an average of about 5'9" (175 cm) for men and 5'3.5" (161 cm) for women. Height in a large population follows a roughly bell-shaped (normal) distribution, so the calculator converts a given height into a z-score — how many standard deviations it sits from the average — and then reads off the corresponding percentile from that curve.
A height at the 50th percentile is exactly average for that sex; the 84th percentile corresponds to one standard deviation above average, and the 16th percentile to one standard deviation below. Because the male and female height distributions don't overlap perfectly, a percentile is only meaningful when compared within the same sex — a 5'9" woman and a 5'9" man are both notably tall relative to their own populations, but by very different margins.
What Actually Determines a Child's Final Height
Genetics sets the outer boundaries of a child's potential height, but several environmental factors decide where within that range they actually land:
- Nutrition, especially adequate protein, calories, and micronutrients like calcium and vitamin D during infancy and the adolescent growth spurt.
- Overall health — chronic illness, untreated hormonal conditions, or repeated severe infections in early childhood can measurably suppress final height.
- Sleep, since growth hormone is released predominantly during deep sleep; a chronically poor sleep schedule during childhood and adolescence can blunt growth over time.
- Puberty timing — earlier puberty generally means an earlier, more concentrated growth spurt followed by an earlier stop, while later puberty allows growth to continue for more years, sometimes producing a taller final height even from a shorter starting point.
Most girls reach close to their adult height by around age 14–15, roughly two years after their first period, while most boys continue growing into their late teens, often not finishing until 16–18. This is also part of why the Khamis-Roche coefficients shift so much with age — a growth spurt that's already happened shows up directly in a child's current height, which the formula can use, while a growth spurt still to come can only be inferred indirectly through genetics and typical timing.
When to Talk to a Pediatrician About Growth
Any prediction here is a useful reference point, not a diagnostic tool. It's worth raising with a pediatrician if a child's height has crossed two or more percentile lines downward on their growth chart, if their tracked growth sits far outside the range either calculator predicts, or if growth velocity slows noticeably for their age without an obvious explanation like the normal pre-puberty slowdown. Any of these can be an early, treatable sign of a growth hormone or other endocrine condition — and a pediatrician has tools neither calculator has, including bone-age imaging and hormone panels, to investigate further.
Frequently Asked Questions
How accurate is the Khamis-Roche method?
Published accuracy is about ±2.2 inches (5.6 cm) for boys and ±1.7 inches (4.3 cm) for girls — tighter than the mid-parental formula alone, since it also uses the child's own current height, weight, and age rather than parental heights only. It's considered the most accurate non-invasive prediction method available without a bone-age X-ray.
How is Khamis-Roche different from the mid-parental formula?
Mid-parental height only averages both parents' heights, which makes it usable from before birth but leaves out everything about the specific child. Khamis-Roche adds the child's own current age, height, and weight on top of both parents' heights, using published age- and sex-specific regression coefficients — this extra information is what tightens the typical error from roughly ±8.5 cm down to about ±4.3–5.6 cm.
Can this calculator predict a baby's or newborn's adult height?
Not with the Khamis-Roche tab, since that method needs a current height and weight reading and is only validated from around age 4 onward. For a baby, newborn, or a pregnancy, use the Parents-Only Estimate tab instead — it only needs both parents' heights.
Why do boys and girls use different formulas?
Adult men average roughly 13 cm (5 inches) taller than adult women, mostly because boys' growth plates stay open about two years longer during puberty. Both the mid-parental formula and the Khamis-Roche coefficients are fit separately by sex to reflect this — the mid-parental method with a flat 13 cm adjustment, and Khamis-Roche with an entirely separate coefficient table for boys and girls at every age.
What's a normal height percentile for an adult?
There's no single "normal" cutoff — height follows a bell curve, so anywhere from roughly the 16th to 84th percentile (within one standard deviation of the US average) covers most adults of a given sex. A height's exact percentile comes from how many standard deviations it sits above or below the sex-specific average — for example, a 6'0" (183 cm) man sits at roughly the 85th percentile among US men.
Is my child's height more affected by genetics or environment?
Research generally attributes about 60-80% of adult height to genetics, with the rest shaped by nutrition, overall health, sleep, and other environmental factors during childhood and adolescence. That's also why every prediction on this page is an estimate rather than a guarantee — the environmental share is large enough to move the outcome by several centimeters either way.
When should I talk to a pediatrician about my child's growth?
Bring it up if your child's height has dropped across two or more percentile lines on their growth chart, if their predicted height is far outside the range calculated here, or if growth velocity slows sharply for their age — any of these can be early signs of a treatable growth or hormonal condition, and a pediatrician has better tools (like a bone-age X-ray) than any online calculator.
How do I convert my height from centimeters to feet and inches?
Divide the centimeter figure by 2.54 to get total inches, then divide that by 12 to get whole feet, keeping the remainder as inches — for example, 175 cm ÷ 2.54 ≈ 68.9 inches, which is 5 feet 8.9 inches. Going the other direction, multiply the feet by 12, add the extra inches, then multiply that total by 2.54 to get centimeters.
This calculator provides general estimates for informational purposes only and is not medical advice. Actual adult height depends on many factors beyond genetics — consult a pediatrician for any specific concerns about a child's growth.