A CUBOID WITH LENGTHS l UNITS, WIDTH w UNITS & HEIGHT h UNITS HAS A VOLUME OF V CUBIC UNITS GIVEN BYV = l*w*h =lwh
Length x width x height = volume
There are formulas for regular shapes. Not all shapes have formulas; for these you can fill them with liquid and measure or weigh the contents.
One way is to cut a small hole in one side of the cuboid, and fill it with water. Then pour the water out into other shapes of equal volume.