21 feet in kilometers

Conversion

21 feet is equivalent to 0.0064008 kilometers.^[1]

Conversion formula
How to convert 21 feet to kilometers?

We know (by definition) that: $1 ft = 0.0003048 km$

We can set up a proportion to solve for the number of kilometers.

\frac{1 ft}{21 ft} = \frac{0.0003048 km}{x km}

Now, we cross multiply to solve for our unknown $x$ :

x km = \frac{21 ft}{1 ft} * 0.0003048 km \to x km = 0.0064008 km

Conclusion: $21 ft = 0.0064008 km$

21 feet is equivalent to 0.0064008 kilometers

Conversion in the opposite direction

The inverse of the conversion factor is that 1 kilometer is equal to 156.230471191101 times 21 feet.

It can also be expressed as: 21 feet is equal to $\frac{1}{156.230471191101}$ kilometers.

Approximation

An approximate numerical result would be: twenty-one feet is about zero point zero one kilometers, or alternatively, a kilometer is about one hundred and fifty-six point two two times twenty-one feet.

Units involved

This is how the units in this conversion are defined:

Feet

The foot is a unit of length in the imperial and US customary systems of measurement. Since 1959, both units have been defined by international agreement as equivalent to 0.3048 meters exactly. In both systems, the foot comprises 12 inches and three feet compose a yard.

Wikipedia page of feet

Kilometers

The kilometre or kilometer (American spelling) is a unit of length in the metric system, equal to one thousand metres (kilo being the SI prefix for 1000). It is now the measurement unit used officially for expressing distances between geographical places on land in most of the world; notable exceptions are the United States and the road network of the United Kingdom where the statute mile is the official unit used.

Wikipedia page of kilometers

Footnotes

[1] The precision is 15 significant digits (fourteen digits to the right of the decimal point).

Results may contain small errors due to the use of floating point arithmetic.

Conversion

Conversion formula How to convert 21 feet to kilometers?

Conversion in the opposite direction

Approximation

Conversion formula
How to convert 21 feet to kilometers?