21 meters in millimeters

Conversion formula
How to convert 21 meters to millimeters?

We know (by definition) that: $1\mathrm{m}=1000\mathrm{mm}$

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

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

Conclusion: 21 ⁢ m = 21000 ⁢ mm

Conversion in the opposite direction

The inverse of the conversion factor is that 1 millimeter is equal to 4.76190476190476e-05 times 21 meters.

It can also be expressed as: 21 meters is equal to $\frac{1}{\mathrm{4.76190476190476e-05}}$ millimeters.

Approximation

An approximate numerical result would be: twenty-one meters is about twenty-one thousand millimeters, or alternatively, a millimeter is about zero times twenty-one meters.