How many miles in 1 km?
There are $1.609\ 344$ kilometers in $1$ mile.
$$\text{Length}_{\text{mi}} = \frac{\text{Length}_{\text{km}}}{1.609\ 344}$$
$$\text{Length}_{\text{mi}} = \frac{1}{1.609\ 344}$$
$$\therefore \ 1\ \text{km} \approx 0.621\ 371 \ \text{mi}$$