What this calculator does
Get a rough idea of how tall a child may grow, based on the parents' heights. Height runs strongly in families. So the easiest way to guess a child's adult height is to start from the parents. The mid-parental method was introduced by the British pediatrician James Tanner. Growth clinics still use it as a quick reference. It averages the two parents' heights. It also adjusts for the fact that men are, on average, about 13 cm (5 inches) taller than women.
Enter the mother's and father's adult heights, and choose whether the child is a boy or a girl. The calculator gives the mid-parental estimate, often called the target height. It also shows a range of about 8.5 cm (3⅓ inches) either side. Most children's adult heights fall within that range.
Where it's used
Why this math matters outside the classroom:
- Curious parents. Parents who are 5 ft 4 in and 5 ft 10 in estimate a son's adult height at about 5 ft 9.6 in.
- Clinic reference. Pediatric clinics compare a child's growth curve with the family's target height range.
- Averages in class. Students average 165 cm and 180 cm, then add 13 and halve: (165 + 180 + 13) ÷ 2 = 179 cm.
- Unit conversion. Learners convert 70 inches to 177.8 cm by multiplying by 2.54 before using the formula.
How to use it
- Choose feet and inches or centimeters.
- Enter the mother's and the father's adult heights, measured without shoes if possible.
- Choose the child's sex.
- Read the estimate and the target range. The working shows each step in centimeters, the unit the method was built in.
What the inputs mean
- Child's sex
- The method adds 13 cm for a boy, or subtracts 13 cm for a girl. That's the typical difference between adult male and female heights.
- Mother's height: feet
- Use measured heights where you can. People often round their own height up by an inch or so. That shifts the estimate by about half as much.
- Mother's height
- Use each parent's adult height, measured without shoes.
Formula and method
boy: target height = (mother + father + 13 cm) ÷ 2 girl: target height = (mother + father − 13 cm) ÷ 2 target range = target height ± 8.5 cm height in cm = (feet × 12 + inches) × 2.54
"Mother" and "father" stand for each parent's adult height in centimeters. The target height is the estimate for the child. The method first puts both parents on an even footing. For a boy, it raises the mother's height by 13 cm, to match a male height. Then it averages that with the father's height. For a girl, it lowers the father's height by 13 cm instead. Both versions boil down to the formulas above.
The ± 8.5 cm band means 8.5 cm above or below the target. It's the range commonly quoted around the target height. Most children end up within it, but some fall outside. Brothers and sisters with the same parents can differ by several inches.
Heights in feet and inches are changed to centimeters using exactly 2.54 cm per inch. The result is changed back and rounded to the nearest tenth of an inch.
Worked example
A mother is 5 ft 4 in and a father is 5 ft 10 in. How tall might their son be?
- Mother: 64 in × 2.54 = 162.56 cm. Father: 70 in × 2.54 = 177.8 cm.
- Boy: (162.56 + 177.8 + 13) ÷ 2 = 353.36 ÷ 2 = 176.68 cm.
- 176.68 cm ÷ 2.54 = 69.56 in, which is 5 ft 9.6 in.
- Range: 176.68 ± 8.5 cm = 168.18 to 185.18 cm, about 5 ft 6.2 in to 6 ft 0.9 in.
Result: The son's mid-parental estimate is about 5 ft 9.6 in (176.7 cm). He'd most likely end up between 5 ft 6.2 in and 6 ft 0.9 in. A daughter's estimate would be about 5 ft 4.4 in.
Understanding the result
Treat the result as what you'd expect from the family, not a prediction for one particular child. Many children finish a few centimeters above or below it.
The estimate doesn't change as a child grows, because it uses only the parents' heights. Methods that also use the child's current height, weight and age can narrow the estimate for older children.
If you have questions about a child's growth, a pediatrician can compare measurements over time with growth charts.
Assumptions and limitations
- Both parents' heights are adult heights, measured accurately.
- The 13 cm adjustment and the ± 8.5 cm range are the standard values for the mid-parental method.
- It doesn't take nutrition, health or activity into account. Nor does it allow for average height rising from one generation to the next.
- It's an estimate only. It isn't medical advice or a diagnosis of any kind.
- Heights outside 120–230 cm (about 3 ft 11 in to 7 ft 6 in) aren't accepted.
Frequently asked questions
How accurate is the mid-parental height?
It's a rough guide. Most children's adult heights land within about 8.5 cm (3⅓ inches) of it. That still leaves a wide band, and some children fall outside it.
Why add or subtract 13 cm?
Adult men are, on average, about 13 cm (roughly 5 inches) taller than adult women. Adding it for a boy, or subtracting it for a girl, turns the other-sex parent's height into a matching one before averaging.
Can I use it for an adopted child or with only one parent's height?
The method relies on height passed down in families. So it only makes sense with both birth parents' heights. With one height missing, there's no reliable substitute.
Is the doubling-height-at-age-two rule better?
It's a different rule of thumb, using the child's own height at about age two. Neither one is precise. The mid-parental method has the advantage of working from birth.
How this calculator is checked
Method: Mid-parental (target) height method attributed to Tanner: (mother + father ± 13 cm) ÷ 2, with a commonly quoted ± 8.5 cm target range. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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