Am I tall, short, or average for my country?

It's the largest pooled height dataset there is, built from surveys run between 1914 and 2014 and modelled forward to the 1996 birth cohort, and it uses only measured heights, leaving out what people say about themselves, which tends to add an inch. Precision isn't even across the map, though. Wealthy countries with long-running health surveys get tight estimates, and some lower-income countries are working from a few small surveys, so treat a percentile there as roughly right rather than exact. The US figures are also checked against the CDC's own measured NHANES numbers.

Because that's how the source surveys record it. They collect and publish height by sex as recorded at birth or in a clinical setting, which is a different thing from gender identity, and the distributions the calculator uses are the male and female ones those surveys defined. No population dataset yet exists with enough non-binary or transgender participants to give a reliable percentile, so rather than invent one the calculator offers the two it can stand behind.

Yes, adults only, which the source datasets define as 18 and over. A child's percentile is a different calculation altogether because it has to be read against an age-specific growth chart: the CDC charts cover ages 2 to 20 in the US and the WHO Child Growth Standards cover infants and children under 5 internationally. Put a 14-year-old's height into this calculator and you'll get a number that means nothing. For babies and toddlers, the baby height percentile calculator uses the proper paediatric references.

The list covers the 20 countries with the best data and the most visitors. If yours isn't there, pick the nearest neighbour in geography and diet: Australia stands in reasonably for New Zealand, and Germany or France for the countries around them. You'll get a rougher answer than someone from a listed country, so read it as a range rather than a point.

Mostly upwards, and fast by the standards of biology. Dutch men grew 20 cm taller between 1870 and 2000, and most countries added around a centimetre a decade through the 20th century as food and public health improved. That climb has stopped in many wealthy countries, and in parts of sub-Saharan Africa some birth cohorts actually lost height during periods of economic or political upheaval. One thing this means for your result: the NCD-RisC figures describe adults born around 1996, so if you're 70 you're being compared with a generation that grew up better fed than yours, and your percentile will read a little low.

Six feet (183 cm) puts an American man at about the 85th percentile, taller than 85 of every 100 adult men in the country, using measured heights from NHANES 2015 to 2018. That's less rare than it feels. Fifteen in a hundred men are six foot or over, so in any decent-sized office you'll find several, even though six foot gets talked about as a threshold for "tall". Move the same man to the Netherlands, where the average is 182.5 cm, and he's at the 51st percentile, bang on ordinary. In Guatemala, where the average is 163.4 cm, he's above the 99th. (Source: Fryar et al. 2021, NCHS Vital and Health Statistics)

It depends entirely on where. The average American man measures 175.3 cm (5 feet 9 inches) in the CDC's NHANES survey for 2015 to 2018, and a British man 175.3 cm, close enough that the two countries share a distribution for practical purposes. Dutch men average 182.5 cm and Danish men 181.4 cm at the top of the table, with Guatemala at 163.4 cm and Indonesia at 163.6 cm near the bottom. Pool every country in the NCD-RisC data and the world's average man is about 171 cm (5 feet 7 inches), a figure almost nobody has in their head because we all calibrate on our own street. These are adults born around 1996. Country averages and the other body measurements are gathered on the body statistics page. (Source: NCD-RisC 2016; Fryar et al. 2021)

American women average 161.3 cm (5 feet 3.5 inches) in the measured NHANES data for 2015 to 2018, and British women 161.6 cm. The tallest women in the world are in Latvia, at 169.8 cm, and the Netherlands, at 168.7 cm, and the global average across every country is roughly 159.5 cm (5 feet 2.8 inches). Women run 11 to 14 cm shorter than men of the same nationality nearly everywhere. Oddly, the gap is narrowest in the countries where girls have historically been fed worst, not because women there are tall but because male height is the more fragile of the two and drops further when nutrition is poor. (Source: NCD-RisC 2016; Fryar et al. 2021)

Around 80%, if the question is why two people in the same country differ. Twin studies comparing identical with non-identical twins put height among the most heritable traits we have, at 87 to 93% for men and 68 to 84% for women in Silventoinen's eight-country comparison, with the remaining 20% coming from childhood nutrition, illness during the growing years and access to healthcare. The catch is that 80% describes differences within one population under similar conditions. Between populations, or across generations, the environmental share does far more work than the number suggests, which is how average heights climbed a centimetre a decade through the 20th century without anyone's genes changing. (Source: Silventoinen et al. 2003, Twin Research; NCD-RisC 2016)

For men, somewhat, and mostly through the height gap between partners. In UK Millennium Cohort couples, Stulp and colleagues (2013, PLOS ONE) found most pairs had a taller man, and couples where the man was shorter, or more than 25 cm taller, turned up less often than chance would predict, though only modestly. What people say they want shows up in real couples, but weakly. (Source: Stulp et al. 2013, PLOS ONE)

If you're over 21, almost certainly not. Boys usually stop between 17 and 21 and girls between 14 and 16, with the timing set by genes and when puberty started, and growth ends for good when the growth plates in the long bones fuse, something a bone-age X-ray can confirm where a birthday can't. From about 30 the direction reverses. Spinal discs compress, muscle tone goes and eventually bone density follows, costing men about 3 cm and women about 5 cm between 30 and 70, and more after that, so a man who measured 180 cm at 30 may measure about 175 cm at 80 and be perfectly healthy. This calculator is for adults 18 and over; children and teenagers belong on the CDC growth charts for ages 2 to 20. (Source: Fryar et al. 2021; Sorkin et al. 1999, American Journal of Epidemiology)