Is km bigger than miles?
The short answer is no. A mile is $1.609\ 344$ kilometers in length.
$$\text{Length}_{\text{km}} = \text{Length}_{\text{mi}} \cdot 1.609\ 344$$
$$\text{Length}_{\text{mi}} = \frac{\text{Length}_{\text{km}}}{1.609\ 344}$$
$$\therefore \ \text{Length}_{\text{mi}} \approx \text{Length}_{\text{km}} \cdot 0.621\ 371$$