RegionBounds

RegionBounds[reg] gives the bounding box for the region.

Examples

Bounds of a disk:

RegionBounds[Disk[{1, 2}, 3]]
(* {{-2, 4}, {-1, 5}} *)

Bounds of a polygon:

RegionBounds[Polygon[{{0, 0}, {2, 0}, {1, 3}}]]
(* {{0, 2}, {0, 3}} *)

Please visit the official Wolfram Language Reference for more details.