How this instrument works
Human height is one of the most routinely converted lengths there is, because the instrument doing the measuring and the form asking for the number often use different systems. A stadiometer in a doctor's office outside North America reads centimetres directly; a US driver's licence application, a growth chart annotation, or an immigration medical form asks for feet and inches. Getting from one to the other means dividing the centimetre reading by 0.3048 metres per foot, keeping the whole feet, and turning the remainder into inches — the same two-step split used for any length, applied here specifically to a person.
The foot used in that division has been fixed at exactly 0.3048 m since 1 July 1959, when the US joined five other English-speaking countries in adopting an international yard of 0.9144 m. Before that agreement, the US foot and the UK foot differed by a few parts per million — far too small to matter for a person's height, but the standardization is what makes today's conversion exact rather than approximate.
Height in feet and inches is also spoken, not just written: a person is described as being '5 foot 7', not '5.58 feet' — mirroring exactly how the Feet and Inches fields below should be read together, as the whole number of feet followed by a smaller inch remainder, rather than as two independent results.
- Enter the measured height in centimetres into the Height (cm) field — it starts at 170 cm as an example.
- Read the Feet field for the whole number of feet in that height, rounded down.
- Read the Inches field for the remainder, given as inches to two decimal places.
- Say or write both fields together, as '5 ft 6.93 in', matching how height is normally spoken aloud.
- For a form asking for whole inches only, round the Inches figure to the nearest whole number first.
Worked example — a 170 cm height on a medical form
A patient measured at 170 cm on a clinic's metric stadiometer needs that height entered in feet and inches on a US intake form. Entering 170 into Height (cm) gives 170 ÷ 100 ÷ 0.3048 = 5.57742782152 feet total. The Feet field floors that to 5, and the Inches field converts the remaining 0.57742782152 feet into inches, 6.92913385827, which the calculator displays as 6.93.
Read together, the patient's height is 5 ft 6.93 in — commonly rounded and spoken as '5 foot 7' in casual conversation, though the form itself should keep the more precise 6.93 in (or a rounded 7 in, per the form's own instructions) rather than silently rounding to a different whole number than the clinic's own record.
Questions
Why are Feet and Inches shown as two separate numbers?
Because height in the US is spoken and written as a compound figure — '5 foot 7', not '5.58 feet'. The Feet field holds the whole number of feet in the measured height; the Inches field holds only what's left over, converted to inches. Reading just one field, or rounding them independently, gives a different (and wrong) answer than reading both together.
Is converting centimetres to feet and inches an exact process?
Yes — the foot has been defined as exactly 0.3048 m since the international yard agreement of 1 July 1959, so there is no measurement uncertainty in the conversion itself, only the rounding shown on screen. A height of 170 cm converts to the same 5 ft 6.93 in every time, with no tolerance to account for.
Should I round 6.93 inches to 7 for a form that wants whole inches?
Follow whatever the specific form instructs, since conventions differ. Many US forms want the nearest whole inch, in which case 6.93 rounds to 7, giving 5 ft 7 in. Others, particularly medical and growth-chart records, prefer to keep the more precise decimal or an eighth-inch reading, since rounding height repeatedly across multiple forms can quietly drift a recorded height by half an inch or more over time.
Why might the Inches field show 12.00 instead of rolling over into an extra foot?
That happens only as a display-rounding artefact: an unrounded value like 11.996 inches rounds to 12.00 at two decimal places, even though the Feet field was correctly floored from the full-precision total before any rounding occurred. The underlying feet-and-inches split is always computed first; the two-decimal display comes afterward.
How is this different from converting a room dimension or product length?
Nothing in the arithmetic changes — a person's height, a ceiling height and a shelf length all convert with the identical centimetres-to-feet-and-inches formula. What differs is only the real-world reading: height is spoken as a single compound figure describing a person, so the two output fields are conventionally combined into a phrase like '5 foot 7' rather than reported as separate measurements.
Do adult height charts anywhere still use a different foot?
No. Every foot in current use, in the US, UK and elsewhere, is the same 0.3048 m international foot fixed in 1959. The only historical alternative, the US survey foot (about 0.3048006 m), was retired for all purposes at the end of 2022 and was never used for describing a person's height in the first place.