Height Converter

Four ways to enter the same height

Height gets written four different ways depending on who is asking. A US doctor's office writes 5 ft 11 in. A growth chart in centimeters wants 180.3. A passport form in Europe wants 1.80 m. A gym app wants 71 inches. All four describe the same body, and getting from one to another is a single multiplication once you know the factor.

This converter takes any of the four, then returns all of them plus two figures that are usually missing: the decimal feet value, which is where most mistakes start, and the chart rounded centimeter value, which is what a nurse writes down.

It is a converter, not a predictor. The height calculator handles the other job, taking a child's current height and the parents' heights to predict adult height, and it also covers height against weight for BMI. If you are measuring something that is not a person, the tree height calculator uses shadow length and angle instead, and the answers there are in feet and meters from a completely different method.

The only number that matters: 2.54

An inch is exactly 2.54 centimeters. Not approximately, and not 2.5. The value was fixed in 1959 when the United States, the United Kingdom and other countries agreed to define the yard as exactly 0.9144 meters, which makes the foot 0.3048 m and the inch 2.54 cm. The NIST Guide to the SI, Appendix B.9 lists inch to centimeter as a boldfaced factor, which marks it as exact.

Two formulas cover every case:

Centimeters = total inches x 2.54. A person 5 ft 11 in is 71 inches tall, so 71 x 2.54 = 180.34 centimeters.

Inches = centimeters / 2.54. Going the other way, 180 centimeters is 180 / 2.54 = 70.87 inches, a shade under 5 ft 11 in.

Meters sit one step further out: divide centimeters by 100, or divide inches by 39.3701. For 71 inches, 180.34 / 100 = 1.8034 meters. That last step is where people drop or add a zero, writing 18.034 or 180.34 for a height that is plainly around 1.8 m.

Feet and inches are not decimal feet

Feet are base 12, and decimal notation is base 10. Writing 5.11 feet means five feet plus eleven hundredths of a foot, which is 5 feet 1.3 inches, not 5 feet 11 inches. The gap is large enough to matter: 5.11 ft is 61.32 inches, and 5 ft 11 in is 71 inches, so the wrong notation loses 9.68 inches, close to eight inches of real height.

The correct decimal is 11 / 12 = 0.9167, so 5 ft 11 in is 5.9167 ft. Six feet is the easy case, because 6.0 ft is exactly 6 ft 0 in, which is why the error hides in every other height.

Any tool that asks for feet as a single number expects the fractional form, so 5 ft 8 in goes in as 5.6667, not 5.8. If a form refuses your height, this is usually the reason.

Quarter inches and the way charts record height

Medical scales measure to the nearest quarter inch or the nearest half centimeter, and growth charts are drawn in those steps. A stadiometer with a sliding headpiece does not report 71.324 inches, and nobody writes that down. Rounding to a quarter inch means four possible values inside each inch, which is why two visits a year apart can show the same recorded height even when the real change is a third of an inch.

In metric, charts round to half centimeters. A measured 71 inches becomes 180.34 cm, which records as 180.5 cm. The conversion does not round to a nicer number on its own, so the rounding step belongs to whoever is filling in the form.

One caution on the last row: a person measured at exactly 6 ft 0 in is 182.88 cm, and half centimeter rounding pushes that to 183.0 cm. A form that then converts back gets 6 ft 0.05 in, which may print as 6 ft 0 in and may print as 6 ft 0.1 in depending on the software.

Three worked examples

The examples below cover the three directions people need: US notation to metric, metric to US notation, and a height that lands between two quarter inch marks.

A 6 ft 2 in player. Start with 6 x 12 + 2 = 74 inches. Then 74 x 2.54 = 187.96 cm, and 187.96 / 100 = 1.8796 m. Charts would record 188.0 cm.

A 1.65 m listing. That is 165 cm, and 165 / 2.54 = 64.96 inches. Divide by 12 to get 5 ft 4.96 in, which rounds to 5 ft 5 in. The metric figure looked like 1.65, and the US figure is not 5 ft 6 in, which is what a quick guess usually produces.

A 150 cm child. That is 59.06 inches, or 4 ft 11.06 in, which records as 4 ft 11 in. The difference between 59.06 and 59 inches is small, but on a growth chart a third of an inch moves a plotted point.

Where US heights sit

The CDC body measurement figures put the measured average height of US adults aged 20 and over at 68.9 inches for men and 63.5 inches for women, from the survey years August 2021 to August 2023. In metric that is 175.0 cm for men and 161.3 cm for women.

Those numbers come from a stadiometer in a mobile exam room, with shoes off and heels against the back plate, and they are averages across every adult age group. Standing next to an average is not a health measure, and the same report shows roughly 10 cm between the 25th and 75th percentile for men, from 170.1 cm to 180.2 cm.

For children, the CDC growth charts plot height by age on curves that use centimeters, which is one reason a pediatric visit reports both numbers. A parent converting a school form from feet to centimeters is doing the same arithmetic as the nurse, just without the stadiometer.

Measure so the number means something

The conversion is exact, but the measurement going into it is not, and that is where most of the error lives. Three habits make a home measurement comparable from one month to the next.

Same time of day. The discs in the spine compress under load through the day, so an evening measurement is usually shorter than a morning one by a small amount. Compare like with like, and do not read a half centimeter drop as a real change.

No shoes, heels together. A rubber sole adds close to an inch, which is more than most people expect. Stand with heels, buttocks and shoulder blades against a wall, look straight ahead, and mark the wall at the top of the head with a book held level.

Feet flat, chin level. Tiptoeing adds height, and tilting the chin up adds a little more. For children under two, length is measured lying down, and that number runs about 1 cm larger than standing height, so a chart that switches methods can show a fake drop.

The converter follows the input you choose, so it cannot fix a measurement taken in socks on carpet. What it can do is remove the arithmetic error, which is the part that turns a good measurement into a wrong number.

Where the conversions go wrong

Four mistakes account for almost every bad height conversion.

Using 2.5 instead of 2.54. The shortcut is close enough for a rough guess and wrong for a record. At 71 inches, 71 x 2.5 = 177.5 cm, which is 2.84 cm short of the right answer. Over six feet the gap grows a little.

Treating inches as decimal feet. 5.11 ft is 61.32 inches, not 71. If a form takes one number for feet, enter the fraction: 5.9167 for 5 ft 11 in.

Dropping a zero in meters. 180.34 cm is 1.8034 m. Typing 18.034 turns an adult into a ceiling height, and typing 180.34 in the meters field turns them into a building.

Rounding twice. Convert, round, then convert back, and the second conversion carries the first rounding error. Round once, at the end, in the unit that gets written down.

None of this needs a service. The factor is exact, the arithmetic fits on one line, and the only judgment call is which rounding convention the form in front of you uses.