Child Height Calculator

Formula

Boy = (father + mother + 13 cm) / 2; Girl = (father + mother − 13 cm) / 2; range ±8.5 cm

The mid-parental height method calculates genetic target height based on biological parents' measurements. The variables include father's height (father) and mother's height (mother), measured in centimeters or converted to equivalent metrics. The constant 13 cm represents the average global sexual dimorphism—the typical physiological height difference between adult males and females. For male offspring, 13 cm is added to the mother's height to align with male genetic potential before averaging with the father's height. For female offspring, 13 cm is subtracted from the father's height to adjust to female genetic potential before averaging. A variance of ±8.5 cm represents the standard statistical margin.

Worked example

Child's sex

m

Father's height

178

Mother's height

165

• Predicted adult height: 178 cm
• In feet and inches: 5 ft 10.1 in
• Likely range (≈95%): 169.5 – 186.5 cm

How the Child Height Calculator Works

Predicting a child's eventual adult stature is a standard component of pediatric developmental tracking. Parents and healthcare providers frequently seek to understand whether a child is tracking along an expected biological trajectory. The Child Height Calculator utilizes the mid-parental height method (often referred to as the Tanner method), an established demographic model in pediatric medicine.

Human adult stature is a polygenic trait, meaning it is governed by the additive and interactive effects of hundreds of genetic variants inherited from both biological parents. Twin and family studies indicate that genetics account for approximately 80% of variation in adult height across well-nourished populations, with environmental influences such as childhood nutrition, sleep quality, and physical health comprising the remaining 20%.

Because biological males and females exhibit different mean heights across global populations—a biological phenomenon termed sexual dimorphism—the calculation must adjust for this discrepancy. Across large-scale demographic studies reviewed by organizations such as the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), the average difference in adult height between biological sexes is approximately 13 centimeters (roughly 5.1 inches).

To balance maternal and paternal genetic contributions on an equitable baseline, the mid-parental formula adjusts one parent's height by 13 cm depending on the child's sex:

• For a biological boy: Maternal height is adjusted upward by adding 13 cm, simulating the height the mother might have attained as a biological male. This adjusted figure is added to the biological father's height, and the sum is divided by 2.
• For a biological girl: Paternal height is adjusted downward by subtracting 13 cm, simulating the height the father might have attained as a biological female. This adjusted figure is added to the biological mother's height, and the sum is divided by 2.

Mathematically, the formulas are expressed as follows:

$$\text{Boy's Predicted Height} = \frac{\text{Father's Height} + \text{Mother's Height} + 13\text{ cm}}{2}$$

$$\text{Girl's Predicted Height} = \frac{\text{Father's Height} + \text{Mother's Height} - 13\text{ cm}}{2}$$

Because genetic inheritance involves random assortment of alleles, children do not inherit identical combinations of parental genes. A child's actual adult height therefore fluctuates around this statistical midpoint. In clinical pediatrics, the target range is typically set at two standard deviations from the mid-parental average, defined as $\pm 8.5\text{ cm}$ (approximately $\pm 3.3\text{ inches}$). Approximately 95% of healthy offspring with no underlying endocrine or nutritional disruptions achieve an adult stature within this target window.

Step-by-Step Worked Example

To see how the formula works in practice, consider the following scenario evaluated using the exact figures from our calculator tool:

• Child's sex: Boy (m)
• Father's height ($fa$): $178\text{ cm}$
• Mother's height ($mo$): $165\text{ cm}$

Step 1: Sum the Biological Parental Heights

First, combine the stature of both biological parents:

$$\text{Combined Height} = 178\text{ cm} + 165\text{ cm} = 343\text{ cm}$$

Step 2: Apply the Sex Adjustment Constant

Because the subject is a biological male, add the $13\text{ cm}$ sexual dimorphism factor to account for the maternal genetic contribution in a male developmental context:

$$\text{Adjusted Sum} = 343\text{ cm} + 13\text{ cm} = 356\text{ cm}$$

Step 3: Divide by Two to Derive Mid-Parental Height

Divide the adjusted sum by 2 to calculate the final point estimate:

$$\text{Predicted Adult Height} = \frac{356\text{ cm}}{2} = 178\text{ cm}$$

Converting $178\text{ cm}$ into imperial measurements yields 5 ft 10.1 in ($178 / 2.54 = 70.0787\text{ inches}$, which equals $5\text{ feet}$ and $10.08\text{ inches}$, rounded to $10.1\text{ inches}$).

Step 4: Calculate the Likely 95% Statistical Range

Apply the standard clinical variance of $\pm 8.5\text{ cm}$ to determine the boundaries of the expected adult stature range:

$$\text{Lower Bound} = 178\text{ cm} - 8.5\text{ cm} = 169.5\text{ cm}$$ $$\text{Upper Bound} = 178\text{ cm} + 8.5\text{ cm} = 186.5\text{ cm}$$

Thus, the tool produces the following exact outputs:

• Predicted adult height: $178\text{ cm}$
• In feet and inches: $5\text{ ft } 10.1\text{ in}$
• Likely range (≈95%): $169.5\text{ – } 186.5\text{ cm}$

How to Interpret Your Results

When evaluating the results generated by the calculator, it is vital to avoid viewing the single point estimate (such as $178\text{ cm}$) as a rigid biological certainty. Rather, it represents the statistical center of gravity for the child's genetic potential.

Understanding the Target Range

The most critical output is the likely range of $169.5\text{ to } 186.5\text{ cm}$. In pediatric healthcare, this range is known as the "target height range." When pediatricians plot a child's continuous measurements on standardized growth charts—such as those published by the CDC or the WHO—they expect the child's growth curve to trend along a percentile that aligns closely with this target range.

• Mid-Range Percentiles: An adult height of $178\text{ cm}$ falls near the 50th percentile for adult males in the United States. A range of $169.5\text{ cm}$ to $186.5\text{ cm}$ encompasses percentiles ranging roughly from the 15th to the 85th percentile.
• Normal Familial Variation: Siblings inheriting genes from the same biological parents can fall at opposite ends of this spectrum due to polygenic recombination. One brother may inherit alleles that place him at $171\text{ cm}$, while another may reach $185\text{ cm}$; both outcomes sit comfortably within normal biological parameters.

Identifying Discrepancies

A projected height helps clinicians spot clinical anomalies early. If a child's documented growth percentile on an official growth curve projects an adult height substantially above or below their calculated mid-parental range, medical providers investigate potential underlying causes, including:

• Constitutional Delay of Growth and Puberty (CDGP): Often called being a "late bloomer," where growth velocity slows temporarily before catching up during a delayed puberty.
• Familial Short or Tall Stature: Where growth follows normal velocity curves, but the absolute height consistently matches the lower or upper limits of genetic expectation.
• Pathological Growth Discrepancies: Including growth hormone deficiency, Turner syndrome, untreated celiac disease, or precocious puberty, all of which alter long-term bone development.

Practical Tips

To ensure you gather accurate baseline data and properly support your child's natural growth trajectory, consider the following clinical and practical recommendations:

1. Standardize Parental Measurements

Self-reported heights are notoriously inaccurate; individuals routinely overestimate stature or report measurements taken in shoes. For an accurate calculation:

• Remove all footwear, hats, and bulky hair ornaments.
• Measure height in the morning using a flat, hard wall and a right-angled object (such as a book or stadiometer) placed firmly against the crown of the head.
• Stand with heels, buttocks, upper back, and occiput touching the vertical surface, with eyes looking straight ahead along the Frankfort horizontal plane.

2. Prioritize Consistent Pediatric Growth Tracking

A single snapshot in time is far less informative than long-term growth velocity (the number of centimeters grown per year). Ensure your child attends regular annual well-child checkups where measurements are systematically plotted on CDC or WHO percentile grids. Sudden flattening or sharp spikes across major percentile lines warrant pediatric consultation.

3. Support Optimal Environmental Health

While genetics establish the developmental boundaries (the upper and lower limits of the target range), environmental variables determine whether a child reaches the peak of that genetic window:

• Deep Sleep: Up to 70% of human growth hormone (HGH) is secreted during deep, slow-wave non-REM sleep. School-age children require 9 to 12 hours of sleep nightly, while adolescents need 8 to 10 hours.
• Balanced Micronutrient Intake: Linear bone growth requires consistent dietary calcium, vitamin D, phosphorus, magnesium, and high-quality protein. Avoid excessive reliance on heavily processed foods lacking bioavailable micronutrients.
• Regular Physical Activity: Weight-bearing exercise, play, and resistance activities stimulate bone mineral density, osteoblast activity, and natural hormonal balance throughout the prepubertal and pubertal years.

4. Recognize When to Seek Clinical Advice

Consult a pediatric healthcare professional if your child grows fewer than 5 cm (about 2 inches) per year between age four and the onset of puberty, if their measured height falls persistently below the 3rd percentile or above the 97th percentile, or if early signs of puberty manifest prior to age eight in girls or age nine in boys.

Comparison

Scenario	Input	Result
Base example	Default inputs	Predicted adult height: 178 cm

Common mistakes

• Measuring parents with shoes on or at different times of day without accounting for spinal compression.
• Using non-biological parental heights, such as adoptive parents or step-parents, which reflect no genetic linkage.
• Assuming the point estimate is an absolute guarantee rather than a statistical midpoint within a ±8.5 cm standard range.
• Failing to account for chronic pediatric illnesses, nutritional deficiencies, or hormonal disorders that alter growth velocity.
• Confusing the mid-parental target height calculation with a clinical bone age assessment conducted via radiograph.

Checklist

• Obtain accurate morning standing heights for both biological parents without footwear.
• Ensure both parental heights are converted into the identical unit of measurement (centimeters or inches).
• Identify the biological sex assigned at birth for the child being evaluated.
• Add 13 cm (or 5 inches) for a boy, or subtract 13 cm (or 5 inches) for a girl.
• Divide the combined parental sum by two to establish the mid-parental genetic target.
• Apply the standard clinical statistical margin of ±8.5 cm (±3.3 inches) to establish the projected range.

Michael Torres

Co-Founder & Chief Editor, Calculators PercentageCo-Founder & Chief Editor

Michael Torres writes about personal finance, loans, and savings for the financial blog The Money Leads.

More about MichaelRead on The Money LeadsLast reviewed: November 13, 2026

This calculator provides an educational statistical estimate based on general population genetics and is not a substitute for clinical growth monitoring. Consult a qualified pediatrician or pediatric endocrinologist for clinical assessments of pediatric growth velocity, nutritional status, or endocrine health.