Height Calculator
Estimate a child's likely adult height from both parents' heights, using the mid-parental height method.
Written by Magesh | Financial Tools & Calculation Specialist · Last updated July 31, 2026
In two sentences: A height calculator using the mid-parental method predicts a child’s adult height by averaging both parents’ heights and adjusting for sex, a formula pediatricians have used since it was first described by Tanner in 1970. This guide breaks down the exact formula, its margin of error, worked examples, and how it compares to the more detailed Khamis-Roche prediction method.
What Is a Height Calculator?
A height calculator predicts a child’s likely adult height using known genetic and growth data. The most widely used approach is the mid-parental height method, which has been a standard procedure for assessing an individual child’s future adult height since it was first described by Tanner in 1970. Pediatricians use this method routinely because it requires minimal information yet provides remarkably accurate predictions.
The Mid-Parental Height Formula
Boys: Predicted Height = (Father's Height + Mother's Height + 13 cm [5 in]) ÷ 2
Girls: Predicted Height = (Father's Height + Mother's Height − 13 cm [5 in]) ÷ 2
For boys, add 13 cm (5 inches) to the combined parents’ height, then divide by two. For girls, subtract 13 cm (5 inches) from the combined height, then divide by two. This adjustment accounts for the average height difference between males and females, since boys and girls follow different growth trajectories through puberty.
The margin of error
For both girls and boys, 8.5 cm on either side of this calculated value represents the 3rd to 97th percentile range for anticipated adult height. The mid-parental height method predicts adult height with approximately 80% accuracy — meaning four out of five children will reach heights within 2 inches of the prediction.
Worked Examples
Example 1: Predicting a son’s height
Father’s height: 178 cm. Mother’s height: 165 cm.
Predicted Height = (178 + 165 + 13) ÷ 2 = 356 ÷ 2 = 178 cm
With an 8.5 cm margin on either side, this boy’s likely adult height range falls between roughly 169.5 cm and 186.5 cm.
Example 2: Predicting a daughter’s height
Same parents: Father 178 cm, Mother 165 cm.
Predicted Height = (178 + 165 − 13) ÷ 2 = 330 ÷ 2 = 165 cm
Notice the predicted height for a daughter (165 cm) is 13 cm lower than for a son (178 cm) from the exact same two parents — entirely due to the sex-based adjustment built into the formula.
Example 3: Using imperial units
Father’s height: 5’11” (71 inches). Mother’s height: 5’5″ (65 inches). For a son:
Predicted Height = (71 + 65 + 5) ÷ 2 = 141 ÷ 2 = 70.5 inches (about 5'10.5")
Step-by-Step: How to Use a Height Calculator
- Measure both parents’ heights accurately — <cite index=”25-1″>always use height without shoes, since shoes can add 0.5 to 2 inches, which would throw off the prediction</cite>.
- Add both parents’ heights together.
- Add 13 cm (5 inches) for a son, or subtract 13 cm (5 inches) for a daughter.
- Divide the result by 2 to get the predicted adult height.
- Remember the roughly ±8.5 cm (±3.4 inch) margin of error — this is a statistical estimate, not a guarantee.
Mid-Parental Height vs. the Khamis-Roche Method
For a more precise prediction, some height calculators use the Khamis-Roche method instead. This method of height prediction was developed in 1994 at Wright State University, and it’s the most accurate method of child height prediction without determining skeletal age — for boys, the margin of error is 2.1 inches, and for girls, the margin is 1.7 inches. The Khamis-Roche method also factors in the child’s current weight, which helps fine-tune the prediction, especially for younger children, and its influence lessens as the child gets older and closer to their adult stature.
<cite index=”21-1″>Note the Khamis-Roche method was developed using research on a group of Caucasian children, so it may be less accurate for children of other ethnic backgrounds</cite> — worth keeping in mind when interpreting results from either method.
What Affects Actual Adult Height Beyond the Formula
- Nutrition — consistent access to balanced, nutrient-dense meals throughout childhood and adolescence supports reaching genetic height potential; chronic malnutrition can suppress it.
- Puberty timing — delayed puberty (no signs by age 13 in girls or age 14 in boys) can affect the growth timeline and final adult height.
- Chronic illness — ongoing health conditions during childhood can affect growth trajectory independent of genetics.
- Bone age — a bone age ahead of a child’s actual age may mean growth will stop sooner than a mid-parental prediction alone would suggest, while a bone age behind actual age may mean more growing time remains.
How to Talk About Height Calculator Results With Your Child
A height calculator prediction is meant to inform, not to set expectations a child feels pressure to meet. Because how parents think about and communicate height predictions affects children’s self-esteem and body image, it’s worth framing a height calculator result as one data point among many, rather than a fixed destiny.
Getting the most value from a height calculator
- Treat the range, not the single number, as the real prediction. A height calculator’s central estimate is a midpoint — the true ±8.5 cm range is the more honest way to think about the result.
- Re-run the height calculator periodically during childhood, especially if using the Khamis-Roche method, since incorporating updated weight and age data can tighten the prediction as a child gets older.
- Use it as a starting point for pediatrician conversations, not a replacement for one — if a height calculator result seems far off from a child’s actual growth trajectory, that’s a reasonable prompt to discuss growth charts with a doctor rather than a cause for concern on its own.
- Remember genetics is only part of the picture. A height calculator captures the genetic contribution well, but nutrition, health, and puberty timing all still play a real role in final adult height.
Frequently Asked Questions
The method predicts adult height with roughly 80% accuracy, meaning about four out of five children land within 2 inches of the prediction, though the true statistical range is closer to ±8.5 cm (±3.4 inches).
This adjustment accounts for the average height difference between adult males and females, since men are, on average, taller than women — the formula builds this population-level difference directly into an individual prediction.
No — the Khamis-Roche method, which also factors in the child’s current height and weight, is generally considered more accurate, with a tighter margin of error than the simpler mid-parental formula, though it requires more input data.
No — the mid-parental method relies specifically on biological parents’ heights as a genetic proxy, so it isn’t applicable when biological parent height data isn’t available.
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In summary, a height calculator using the mid-parental formula gives parents a scientifically grounded, quick estimate of a child’s likely adult height, and understanding both the formula and its roughly ±8.5 cm margin of error helps put any individual prediction in proper context.
About the author: Magesh is a Financial Tools & Calculation Specialist focused on building and fact-checking online calculators across finance, health, and everyday measurement topics.
Note: This calculator and article are provided for general educational and informational purposes only and do not constitute medical advice. Height predictions are statistical estimates with a meaningful margin of error. Consult a pediatrician for clinical growth evaluation and any concerns about a child’s growth pattern.