Unit Converters
Height in Feet and Centimetres: Mixed Units
Convert a height written in feet and inches into centimetres, decode decimal feet, and show how whole-inch rounding changes a height record.
Start with the notation used for height
Human height is often written as feet followed by an inch remainder, such as 5 ft 7 in. Convert the feet to inches, add the remaining inches, and multiply the total by 2.54. For this example, 5 × 12 + 7 = 67 inches, and 67 × 2.54 = 170.18 cm. The original notation gives two parts of one length. It does not mean 5.7 decimal feet, and it should not be entered as a bare 5.7 in a field whose unit is feet.
Show the decimal-foot alternative
Five feet seven inches equals 5 + 7/12 = 5.583333... feet. Multiplying that value by 30.48 cm per foot also gives 170.18 cm. By contrast, 5.7 feet means 5 feet plus 0.7 × 12 = 8.4 inches, which equals 173.736 cm. The difference between these examples is 3.556 cm. A data form with one decimal feet field and a form with separate feet and inches fields therefore need different entries for the same person's measured height.
Convert centimetres back into a familiar form
For a record of 165 cm, divide by 2.54 to get approximately 64.96063 inches. That is 5 feet plus approximately 4.96063 inches, which rounds to 5 feet 5 inches at whole-inch precision. Converting the rounded 65 inches back gives 165.10 cm. Preserve the original 165 cm if subsequent calculations need its stated precision, and use the rounded mixed-unit form as a display value. Repeatedly overwriting a measurement with rounded conversions can gradually lose the original information.
Keep conversion separate from interpretation
Height conversion says nothing by itself about an ideal body weight, body mass index or a growth percentile. Those calculations need other information and, where relevant, age-specific interpretation. It also cannot reconcile measurements taken with different footwear or posture. If two records differ, compare their measurement method and rounding before assuming the units are responsible. Label a stored value as centimetres, decimal feet or feet-and-inches so a later reader does not have to infer the format from the number alone.
Use exact unit definitions without implying exact measurement
The international inch is exactly 2.54 centimetres, and one foot is exactly 12 inches or 0.3048 metres. These fixed relations let a converter change units without knowing the object being measured. The measurement itself may still be approximate. A tape marked in whole millimetres does not produce a more accurate measurement merely because the converted number has six decimal places. Retain enough digits during the calculation, then report a sensible precision for the original reading and the intended use of the converted dimension.
Keep a mixed measurement separate from a decimal
Feet and inches use a base of twelve inches per foot, whereas decimal feet use tenths and hundredths of a foot. Thus 5 feet 6 inches is 5.5 feet, not 5.6 feet. To combine a mixed measurement, multiply the whole feet by 12 and add the remaining inches. To split a decimal-foot result, take its whole-number part as feet and multiply the fractional part by 12 to obtain inches. If rounded inches reach 12, carry them into the next whole foot rather than writing an unusual twelve-inch remainder.
Choose matching input and output quantities
The linked length converter has a numeric value and From and To unit selectors. Enter a single numerical quantity, not a phrase containing feet and inches; combine mixed units first. Check the output label before copying the result into a drawing or form. A length conversion does not calculate area, circumference or fit. If a problem involves two dimensions, convert each separately. For an area, the length factor must be squared; for volume, it must be cubed. Applying the linear factor once to a square or cubic unit produces the wrong scale.
Calculator for the supported step
Enter the combined length as one number, choose its original unit under From and the requested unit under To, and calculate. The displayed decimal length may need the mixed-unit formatting explained above.
Sources and method
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