Child Height Predictor · Practical guide
Mid-Parental Height Formula Explained
The simple formula pediatricians use to estimate a child's adult height, in inches and centimeters, with worked examples.
At a glance
The formula
The mid-parental height formula estimates a child's genetic target height from the parents' heights. In inches: for a boy, predicted height = (mother's height + father's height + 5) ÷ 2. For a girl, predicted height = (mother's height + father's height − 5) ÷ 2. The result comes with an expected range of plus or minus 2 inches. In centimeters, the constant is 13 instead of 5: add 13 cm for a boy, subtract 13 cm for a girl, with a range of ±5 cm.
Interactive tool
Child Height Predictor
Enter your own values, then compare the result with the examples below.
Predicted Adult Height
Worked example in inches
Mother 5'5" (65 in), father 5'10" (70 in). For a son: (65 + 70 + 5) ÷ 2 = 140 ÷ 2 = 70 inches (5'10"), likely range 68-72 inches. For a daughter: (65 + 70 − 5) ÷ 2 = 130 ÷ 2 = 65 inches (5'5"), likely range 63-67 inches.
Worked example in centimeters
Mother 165 cm, father 180 cm. For a son: (165 + 180 + 13) ÷ 2 = 358 ÷ 2 = 179 cm, likely range 174-184 cm. For a daughter: (165 + 180 − 13) ÷ 2 = 332 ÷ 2 = 166 cm, likely range 161-171 cm. The calculator above handles both units and applies the correct constant automatically.
Why the 5-inch (13 cm) adjustment
Adult men average about 5 inches taller than adult women. The constant shifts the mid-parental average up for boys and down for girls so the prediction lands on the correct gender's curve. Without it, daughters of tall parents would be systematically overestimated and sons underestimated.
Where the formula comes from
The method dates back to 19th-century researcher Francis Galton and was refined into its modern form by pediatric growth researchers. It remains the standard first-pass estimate in pediatric endocrinology because it requires nothing more than two measurements, yet lands within 2 inches of actual adult height for the majority of children.
Frequently Asked Questions
What is the mid-parental height formula in one line?
Add the mother's and father's heights, add 5 inches (13 cm) for a boy or subtract 5 inches (13 cm) for a girl, then divide by 2. The range is plus or minus 2 inches (5 cm).
Why do boys and girls use different constants?
The 5-inch (13 cm) adjustment reflects the average height gap between adult men and women. It shifts the parents' average onto the correct growth curve for the child's gender.
Does the formula work for all ethnicities?
It works as a general estimate across populations, but average heights differ between population groups, so predictions can run slightly high or low for some families. It is best treated as a rough target.
Can doctors predict height more precisely?
Yes. A bone age X-ray of the hand and wrist, combined with current height and growth velocity, produces a tighter prediction than the mid-parental method alone. That requires a pediatrician or endocrinologist.