Radius and Diagonal Lines

Circles are squares in 5e's standard rules (just like movement): https://www.youtube.com/watch?v=i4rg2L61kXw

The Token Method creates a square based off the standard diagonal rules in 5e, as moving in any direction on a grid is supposed to cost 5 feet of movement.

Optional Rules: Diagonals

When measuring range or moving diagonally on a grid...

Just about everyone plays with variant rules where diagonal movement costs 5 movement, then 10 movement, and then repeat that process -- essentially every other diagonal movement costs 10 feet.