Volume

Volume[reg] gives the volume of a three-dimensional region.

Examples

Volume of a ball:

Volume[Ball[{0, 0, 0}, r]]
(* (4 Pi r^3)/3 *)

Volume of a cylinder:

Volume[Cylinder[{{0, 0, 0}, {0, 0, 1}}, 1]]
(* Pi *)

Please visit the official Wolfram Language Reference for more details.