How do you convert square miles into square kilometers?

Multiply square km by 0.39 to get approximate square miles.

Formula: square miles x 2.6 = square kilometers.

1 mi² = 2.58998 km²

You take the square root. Use a calculator. It's usually the 2nd function for the button that squares a number.

You can't. Miles measure distance (one dimension) whereas square miles measure area (two dimensions).