Height Calculator

Using the height calculator

The tool has two modes, chosen with Calculator mode. Height predictor estimates a growing child's final height from three facts: sex, age and current height. Height conversion changes a height between metric and US units.

1. Pick the unit system, US (feet and inches) or metric (centimetres or metres).
2. In predictor mode choose male or female, enter the age as complete years and pick the remaining months. Use zero in both for a newborn.
3. Enter the current height. A measurement taken without shoes, standing against a wall, is more reliable than a guess.
4. Press Calculate Adult Height. The answer appears in both unit systems.

The prediction accepts current heights from 40 to 200 cm (about 1 ft 4 in to 6 ft 7 in) and ages up to 18 years and 3 months. Beyond that, a person is treated as fully grown, and the calculator tells you so.

How the adult height is predicted

The predictor uses the multiplier method, published by Paley and colleagues in 2004. Researchers took growth-chart data and worked out, for each age and sex, the number by which a child's current height must be multiplied to give the height they will reach as an adult. The multiplier shrinks as the child gets closer to full height.

predicted adult height = current height × multiplier(age, sex)

The multiplier table has an entry every 3 months until age 2 and every 6 months from then on, so a child's age is matched to the nearest entry. A boy of 8 years 1 month uses the 8 years 0 months multiplier, and one aged 8 years 4 months uses the 8 years 6 months entry. If the age falls exactly halfway between two entries, the younger entry is used.

Girls have smaller multipliers than boys at the same age because they reach their final height earlier and are, on average, shorter as adults. By about 17 years the girls' multiplier is essentially 1.000.

How accurate is the prediction?

No predictor is exact. In the study that introduced the multiplier method, which tested it on children followed from childhood to adulthood, predictions for boys were typically within 1.4 to 4.3 cm of their final height depending on age. About 85 percent were within 5 cm (2 in) and nearly all were within 7.5 cm (3 in). Girls' predictions were less tight: roughly two in three landed within 5 cm and about five in six within 7.5 cm. Accuracy dips in the early teens, when growth spurts begin at very different ages in different children.

Treat the result as a likely range of a few centimetres either side, not a promise. The method assumes a child with normal growth. Medical conditions that affect growth make the figure unreliable, so discuss any concern about a child's growth with a paediatrician.

Other ways to predict adult height

• Bone-age methods such as Bayley-Pinneau, Roche-Wainer-Thissen and Tanner-Whitehouse compare an X-ray of the hand with reference images to judge how much growing is left. They need a clinic visit, and bone-age readings differ between observers.
• Khamis-Roche uses the child's height and weight together with both parents' heights. It was developed on white American children, so it does not suit every family.
• Mid-parental height averages the parents' heights and adds 6.5 cm for a boy or subtracts 6.5 cm for a girl, which is the same as (father + mother ± 13 cm) ÷ 2. It ignores the child's own growth so far and tends to pull tall or short families toward the average.

The multiplier method needs none of those inputs, which is why it works for children of any background without parent data.

What influences final height

Genes account for most of the variation between people, but several things can stop a child from reaching their genetic potential:

• Nutrition. Long-term shortage of energy, protein, iron, zinc or vitamin D slows growth. The calorie calculator gives a rough idea of energy needs.
• Hormones. Growth hormone and thyroid hormone both matter, and too little or too much of either changes the outcome.
• Chronic illness. Coeliac disease, inflammatory bowel disease, chronic kidney disease and early arthritis can all hold growth back.
• Genetic conditions. Turner, Down and Marfan syndromes, among others, alter growth patterns.
• Timing of puberty. An early puberty brings a fast spurt but an earlier stop, while a late one gives more time to grow.

This calculator gives a statistical estimate for general information. It is not medical advice and does not replace a paediatrician's assessment of a child's growth. See the disclaimer.

Average adult height in the United States

National health surveys put the average American adult man at roughly 175 cm (5 ft 9 in) and the average adult woman at roughly 162 cm (5 ft 4 in). The gap of 13 cm or so between the sexes is the reason sex is part of any height prediction. To see where a specific measurement falls against others of the same age and sex, use the height percentile calculator, and to picture two heights side by side try height comparison.

Converting between height units

In conversion mode the calculator applies two fixed relationships: 1 inch is 2.54 cm, and 1 foot is 30.48 cm.

feet = centimetres ÷ 30.48

centimetres = (feet × 12 + inches) × 2.54

Example: 185 cm ÷ 30.48 = 6.07 ft. In inches that is 185 ÷ 2.54 = 72.8, which rounds to 73 in, or 6 ft 1 in. Going the other way, 6 ft 3 in is (6 × 12 + 3) × 2.54 = 190.5 cm.

For a dedicated tool that converts as you type, see the height converter.