21 centimeters in kilometers

Conversion formula
How to convert 21 centimeters to kilometers?

We know (by definition) that: $1\mathrm{cm}=1e-05\mathrm{km}$

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

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

Conclusion: 21 ⁢ cm = 0.00021 ⁢ km

Conversion in the opposite direction

The inverse of the conversion factor is that 1 kilometer is equal to 4761.90476190476 times 21 centimeters.

It can also be expressed as: 21 centimeters is equal to $\frac{1}{\mathrm{4761.90476190476}}$ kilometers.

Approximation

An approximate numerical result would be: twenty-one centimeters is about zero kilometers, or alternatively, a kilometer is about four thousand, seven hundred and sixty-one point eight nine times twenty-one centimeters.