21 millimeters in inches

Conversion formula
How to convert 21 millimeters to inches?

We know (by definition) that: $1\mathrm{mm}\approx 0.039370079\mathrm{in}$

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

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

Conclusion: 21 ⁢ mm ≈ 0.826771659 ⁢ in

Conversion in the opposite direction

The inverse of the conversion factor is that 1 inch is equal to 1.20952380952381 times 21 millimeters.

It can also be expressed as: 21 millimeters is equal to $\frac{1}{\mathrm{1.20952380952381}}$ inches.

Approximation

An approximate numerical result would be: twenty-one millimeters is about zero point eight three inches, or alternatively, a inch is about one point two zero times twenty-one millimeters.