Height Calculator (Child Height Predictor)

What Is Mid-Parental Height?

Everything on this page rests on one quantity: the average of two parents' heights, shifted up or down for the child's sex. Pediatric practice calls the shifted figure the target height, and treats it as a band to check a growing child against rather than as a forecast standing on its own.

The idea comes from a 1970 paper by Tanner, Goldstein and Whitehouse in Archives of Disease in Childhood, which published height standards for children aged 2 to 9 that allowed for the heights of their parents. A short child of short parents and a short child of tall parents are not the same clinical finding, and a chart that never asks about the parents cannot tell them apart.

What the calculator hands back is a reference point rather than a destination. A 2024 study in Children looked at 23 unusually large nuclear families — a mean of 11 adult children each — and found that standard sex-adjusted mid-parental height explained 36 percent of the variation in the children's adult heights. The other 64 percent sat inside families whose parental average was, by construction, identical for every sibling.

Target Height, Mid-Parental Height, and Predicted Height

Three terms circulate for closely related quantities, and separating them saves confusion. Mid-parental height, strictly, is the raw average of the two parents with no adjustment at all: 172.5 cm (5′8″) for a 165 cm mother and a 180 cm father. Target height is that average after the sex offset has been applied, and it is the number this page returns. Predicted adult height, in a clinical setting, usually means something else entirely — a projection built from the child's own measurements and skeletal maturity, which no parent-only formula attempts.

This tool does the middle one. It never asks for the child's current height, age or weight, so it cannot be projecting anything forward from the child. It is describing a pair of parents and labeling the description with the child's sex.

Where the 6.5 cm Offset Comes From

The offset is half the average adult height difference between men and women, which sits near 13 cm in the populations these standards were built on. Split evenly, a boy is placed 6.5 cm (2.6 in) above the parental average and a girl 6.5 cm below, so a son's estimate and a daughter's estimate from the same parents always differ by exactly 13.0 cm.

Silventoinen's eight-country twin study gives a sense of how steady that gap is across quite different populations. Mean adult height there ran 184 cm for men and 171 cm for women in the Netherlands, and 177 cm and 163 cm in Italy: a 13 cm gap in the first and 14 cm in the second, even though the Dutch men averaged 7 cm taller than the Italian men.

The same fixed number is also the offset's weakness. One value is applied to every family that uses the method, so a population whose real adult gap is 11 cm or 15 cm still receives 6.5.

How Do You Calculate a Child's Adult Height?

One average and one offset. There is no age term, no weight term and no table to look up, which is what makes the method usable in a two-minute appointment and also what limits what it can tell you.

Boy:  (mother's height + father's height) ÷ 2 + 6.5 cm
Girl: (mother's height + father's height) ÷ 2 − 6.5 cm

Likely range: estimate − 8.5 cm  to  estimate + 8.5 cm

The Mid-Parental Height Formula, Written Out

Both heights have to be in the same unit before they can be averaged, and the calculator settles that with a single control: pick Centimeters or Feet + inches once, and both fields are read that way.

Mid-parental average = (mother's height + father's height) ÷ 2

Son's estimate      = mid-parental average + 6.5 cm

Daughter's estimate = mid-parental average − 6.5 cm

Likely range        = estimate ± 8.5 cm

Nothing else enters. Because the two parents are added together before anything else happens, only their sum matters — which parent is which makes no difference, and neither does how the same total is split between them. A 170 cm mother with a 170 cm father, a 160 cm mother with a 180 cm father and a 140 cm mother with a 200 cm father all return the identical 176.5 cm (5′9″) for a son.

Step by Step

Four controls, in the order the form presents them.

• Choose Boy or Girl. This picks the sign on the 6.5 cm offset; nothing else about the calculation changes.
• Choose the height unit — Centimeters, or Feet + inches written as 5.4 for 5 ft 4 in.
• Enter the mother's height in the unit you just chose.
• Enter the father's height in the same unit.
• Press Calculate.

Boy and Centimeters are preselected; the two height fields open empty. Because they open empty, the page works nothing out on arrival, and it does not recalculate while you type — the answer appears when you press Calculate, and again each time you press it after changing something. Reset returns the panel to its empty state.

Worked Example: a 165 cm Mother and a 180 cm Father

Child's Sex set to Boy, Height Unit on Centimeters, mother 165, father 180.

Mid-parental average = (165 + 180) ÷ 2 = 172.5 cm

Son's estimate = 172.5 + 6.5 = 179.0 cm

Range = 179.0 − 8.5  to  179.0 + 8.5 = 170.5 to 187.5 cm

Predicted adult height

179.0 cm (5′10″)

Underneath that readout the panel prints "Likely range: 171–188 cm (5′7″–6′2″) — most children land inside it", rounding each end of the band to a whole centimeter for display. The line above it restates the arithmetic as "Mid-parental method: (165 + 180) ÷ 2 + 6.5 cm for a boy", which is the fastest way to confirm the unit selector was where you meant it to be.

The Same Parents, a Daughter

Switch the first control to Girl and change nothing else. The average holds at 172.5 cm; the offset flips sign.

Daughter's estimate = 172.5 − 6.5 = 166.0 cm

Range = 166.0 − 8.5  to  166.0 + 8.5 = 157.5 to 174.5 cm

Predicted adult height

166.0 cm (5′5″)

Her panel shows "Likely range: 158–175 cm (5′2″–5′9″) — most children land inside it". The 13.0 cm separating 179.0 from 166.0 is the whole of what the child's sex contributes here, and it is the same 13.0 cm whichever pair of parents you enter.

Entering Feet and Inches

The Feet + inches option reads the digits after the decimal point as whole inches, not as a fraction of a foot. The selector label spells the convention out — 5.4 = 5 ft 4 in — and overlooking it is the quickest route to a wrong answer on this page.

Typing 5.1 for a mother who is five foot ten is the expensive version of that slip. With the father entered as 6.2, the readout says "189.4 cm (6′3″)" when she is entered as 5.10 and "177.9 cm (5′10″)" when she is entered as 5.1 — the estimate falls 11.4 cm, four and a half inches, on one missing zero. Inches above eleven are clamped rather than carried over, so 5.12 is read as 5 ft 11 in and gives exactly the same answer as 5.11.

Mismatching the selector is caught for you rather than answered wrongly. Type 165 while the unit still reads Feet + inches and it is read as 165 feet, far outside what the tool accepts, so the amber notice appears instead of a number. Type 5.4 while the unit reads Centimeters and 5.4 cm fails the same way at the bottom end.

One display quirk is worth knowing before you compare the lines against each other. In feet-and-inches mode the second line of the panel rounds each parent to a whole centimeter before printing it, so a 5.4 mother and a 5.11 father appear as "Mid-parental method: (163 + 180) ÷ 2 + 6.5 cm for a boy". The estimate itself is computed from the unrounded 162.56 and 180.34 and comes back as 177.9 cm, not the 178.0 that line implies. The large readout is the accurate one.

Height Chart: Predictions by Parent Height

Every figure in these charts came out of the calculator on this page.

Read the mother's height down the left and the father's along the top. Cells are the estimate for a son, in centimeters. Because only the sum of the two parents enters the formula, the same value repeats along every diagonal — which is why 155 with 190 and 175 with 170 both land on 179.0.

The grid runs from 164.0 cm (5′5″) in the top-left corner to 189.0 cm (6′2″) in the bottom-right — 25 cm of spread across a 25 cm span in each parent. Every cell carries the same silent ±8.5 cm, so the bottom-right corner's band still reaches down to 181 cm and the top-left corner's still reaches up to 173.

Height Chart for Girls

The identical grid for a daughter. Each cell is exactly 13.0 cm below its counterpart above, because that is the only thing the sex control changes.

Between them the two charts span 151.0 cm to 189.0 cm, and every value in that span is the correct output for the parents beside it. A prediction quoted without the parents it came from carries almost no information.

What One Centimeter of Parent Is Worth

Because the two heights are averaged, each parent's contribution is halved before the offset is applied. That makes the arithmetic of a measurement error easy to follow.

A centimeter on either parent moves the estimate half a centimeter, so knowing a height only to the nearest inch — an error of at most 1.3 cm on that parent — costs about 0.6 cm on the answer. Against a likely range 17 cm wide, that is noise. The control that genuinely matters is the sex selector, worth 13.0 cm on its own, which is more than a 25 cm difference between two fathers would move it.

Notice what is missing from that table: there is no entry for the child's age, none for how tall the child is now, and none for how tall the grandparents were. None of those are inputs, so none of them can move the number.

Centimeters to Feet and Inches

The calculator converts its own answers using whole inches, rounding to the nearest one, so 179.0 cm prints as 5′10″ and 172.5 cm as 5′8″. The strip below is that same conversion applied across the range these charts cover.

Rounding to the nearest inch is why two estimates 0.5 cm apart can share a label or straddle one: 179.0 cm shows as 5′10″ while 179.5 cm shows as 5′11″, a whole inch of apparent movement from half a centimeter of real change. Compare the centimeter figures when you are comparing two predictions.

Using the Free Height Calculator Online

The tool at the top of this page is free, needs no sign-in and runs one short formula. Pressing Calculate loads a small formula module into the browser and does the arithmetic there, so no server round trip sits between your entry and the answer.

• Child's Sex — Boy or Girl
• Height Unit — Centimeters, or Feet + inches (5.4 = 5 ft 4 in)
• Mother's Height — in the unit selected
• Father's Height — in the unit selected

Four controls, two of which carry measurements. There is no field for the child, no choice of prediction method and no growth chart. The page performs one calculation and returns one estimate with one range attached.

What the Result Panel Shows

The panel is headed Predicted Adult Height and returns four lines. For a boy with a 165 cm mother and a 180 cm father they read as follows.

• 179.0 cm (5′10″) — as the large readout
• Mid-parental method: (165 + 180) ÷ 2 + 6.5 cm for a boy
• Likely range: 171–188 cm (5′7″–6′2″) — most children land inside it
• Genetics isn't destiny: nutrition, health, and timing of puberty all matter — a pediatrician's growth-chart tracking beats any formula

The second line deserves a glance rather than a skim, because it is the only place the numbers the formula actually used are visible. In centimeters it repeats what you typed. In feet-and-inches mode it shows the converted values instead, rounded to whole centimeters, which is how you catch a 5.1 that should have been 5.10.

A Copy result button below the readout puts all four lines on the clipboard as plain text. If either height falls outside what the formula accepts, the panel turns amber under a Check your inputs heading and shows a single message — "Enter both parents' heights" — in place of a number, whichever field caused it.

What the Calculator Does Not Ask For

Knowing what is absent tells you which claims about the answer are safe to make.

• No age for the child — the estimate is the same whether the child is two or fourteen
• No current height or weight for the child, so nothing is being extrapolated from a growth curve
• No bone age, which is the measurement clinical height prediction is usually built on
• No grandparents, no birth weight, no country, no ethnicity
• No option to average more than two parents, or to enter one

That last one is a real constraint rather than a quibble: both fields must be filled and both must clear the accepted range, so a single known parent cannot be entered alone. Putting the one known height into both fields is not a workaround either — it returns the estimate for two parents of that height, which is a different family.

Where a child stands against peers right now is the measurement pediatricians weigh more heavily than any parent-based prediction, and it is a different calculation entirely — that one is the Height Percentile Calculator.

How to Read Your Result

You are given two numbers that behave very differently. The estimate is a single point, and its precision to one decimal place is an artifact of the arithmetic rather than a claim about the child. The range is the part carrying the actual information.

The Range Is the Result

Eight and a half centimeters either side is 3.3 inches, and 17 cm end to end is just under seven. For the worked example the band runs 171 to 188 cm, printed as 5′7″ to 6′2″. Set that against the twin-study averages quoted earlier — 177 cm for men in Italy, 184 cm in the Netherlands — and the son's band swallows both national means and still has room above the taller one. A prediction that wide is not going to settle an argument about whether a boy will make the basketball team.

Read it as a target zone instead. If a child's own growth curve is tracking toward the middle of that band, the parents' heights and the child's measurements are telling the same story. If the curve is heading well outside it, that disagreement is the useful signal — and it is a signal about the child, not about the formula.

The band is applied as a flat 8.5 cm to every result, incidentally. It does not widen for unusually short or unusually tall parents, and it does not narrow when the two parents happen to be the same height.

Checking the Estimate Against Where the Child Is Now

Growth is read as a curve, not a point. The WHO height-for-age reference for ages 5 to 19 publishes exactly that: charts and tables in z-scores and percentiles, separately for girls and boys, which is what a clinician plots a series of measurements against. A child who holds the same percentile line year after year is doing what the chart expects; a child crossing lines downward is the pattern that prompts a closer look.

MedlinePlus describes the shape of that curve plainly — from ages 2 to 10 a child grows at a steady pace, and a final growth spurt begins at the start of puberty, somewhere between ages 9 and 15. Two measurements taken either side of that spurt will disagree wildly about where a child is heading, which is why a single height on a single day is worth much less than the line joining several.

Deep sleep is when growth hormone is released in its strongest pulses, and how many hours a child that age should be getting is set out by age on the Sleep Calculator.

When the Number Warrants a Conversation

The estimate is not a screening test, but a few patterns are worth raising with a pediatrician rather than resolving with a calculator.

• A child whose current percentile line is drifting downward across the chart rather than following it.
• A child sitting well outside the ±8.5 cm band that both parents' heights point to, in either direction.
• Puberty starting outside the usual window — the NICHD puts the typical onset at ages 8 to 13 in girls and 9 to 14 in boys, and defines precocious puberty as beginning before 8 in girls or before 9 in boys.
• A growth spurt that finished noticeably earlier than peers, since early maturation can mean growth halts too soon.

What a clinic can add is the measurement this page has no access to. A hand x-ray reads a child's bone age, which MedlinePlus describes as a way to find out whether a health problem is preventing normal growth, or how much growth is left. That last phrase is the difference between a formula and an assessment: bone age looks at the child in front of it, while the mid-parental method only ever looked at two adults.

Limits: When This Method Does Not Apply

The page prints a figure to one decimal place, and that precision is not earned by the method behind it. Four limits sit between this estimate and a child's actual adult height, and only the last one is visible on the form.

It Describes the Average Child of These Parents

The formula has no way to distinguish one sibling from another, because nothing about the individual child is entered. Every child of the same two parents and the same sex receives the identical number, and real families do not cooperate with that. The 2024 study behind the 36 percent figure chose its 23 families precisely because each had many adult children — a mean of 11 — so the spread within a single set of parents could be measured directly.

This is the honest reading of the ±8.5 cm band: it is not measurement uncertainty in the parents' heights, which the sensitivity table shows would be worth well under a centimeter. It is the spread among children who share one prediction.

The Method Tends to Run Low

Sex-adjusted mid-parental height is not just imprecise, it is slightly biased. In that same 2024 analysis the children came out on average 2.7 cm taller than their target heights predicted. Correcting for the parents' ages, using a multiplicative rather than additive sex adjustment and allowing for regression to the mean cut the bias from 2.7 cm to 0.14 cm — none of which this calculator does, because it runs the standard version.

There is a straightforward reason a parent-based estimate would lag. Adult height has been rising for generations: the NCD Risk Factor Collaboration reanalyzed 1,472 population studies covering more than 18.6 million people born between 1896 and 1996 across 200 countries, and found gains of 20.2 cm in South Korean women and 16.5 cm in Iranian men over that century, alongside very little change in parts of sub-Saharan Africa and South Asia. Where heights are still climbing, a formula anchored to the parents' generation predicts the parents' generation.

Take the 2.7 cm as a direction rather than a correction to apply by hand. It came from one cohort of unusually large families, and the fix its authors proposed is a different formula, not an offset bolted onto this one.

Both Parents, Not One — and Not Only Genes

There is no parent who determines a child's height, and the formula's even split is the closest simple statement of why. Height is polygenic on a scale that took a genome-wide association study of 5.4 million people to map: 12,111 independent variants, clustered in 7,209 genomic segments covering about 21 percent of the genome, together accounting for 40 percent of the variance in adult height in populations of European ancestry and only around 10 to 20 percent in populations of other ancestries.

Heritability is high but not total, and it is not uniform. The eight-country twin study put heritability of adult height at 0.87 to 0.93 among men, and lower and more variable among women at 0.68 to 0.84, with the difference traced mainly to shared environment mattering more in the women's data. Whatever share is left is where nutrition, illness and the timing of puberty do their work — and a formula built on two numbers cannot see any of it.

The practical version: adequate nutrition and health let a child reach the range their genes allow, and deficiency can cost real centimeters, but surplus food does not push anyone past the top of that range. The century-scale gains above are what happens when whole populations stop being deficient, not what happens when one child eats more.

Adoption, Donor Conception, and a Parent You Cannot Measure

The method needs two biological parents' heights and has no substitute for either. Adoptive and step-parents' heights carry no information here, and entering them produces an arithmetically valid answer about the wrong two adults. The same applies to donor conception where the donor's height is unrecorded.

Guessing is defensible only if you are honest about the width it adds. A guess wrong by 5 cm moves the estimate 2.5 cm, which is small against a 17 cm band; a guess wrong by 15 cm moves it 7.5 cm, which is most of the band's half-width. Where one parent's height is genuinely unknown, growth-chart tracking of the child is the better instrument, and it does not need the parents at all.

The Heights the Tool Will Accept

Two ranges are enforced before the formula runs, and they are not identical for the two parents.

Anything outside those bounds — or either field left blank — produces the same amber notice reading "Enter both parents' heights", with no indication of which entry was at fault. A mother at 221 cm is rejected while a father at 230 cm is accepted, so if the notice appears on what look like plausible numbers, check the mother's field first.

Inside those bounds the tool will calculate anything, including pairings no family occupies. It holds no opinion about whether your entries are plausible, and it applies the same 6.5 cm offset and the same 8.5 cm band to all of them.