Measuring Distance
As a general rule, distance is measured assuming that 1 square equals 5 feet.

Diagonals: When measuring distance, the first diagonal counts as 1 square, the second counts as 2 squares, the third counts as 1, the fourth as 2, and so on.

You can't move diagonally past a corner (even by taking a 5-foot step). You can move diagonally past a creature, even an opponent.

You can also move diagonally past other impassable obstacles, such as pits.