Why is the volume of a 12 sided object measured in cubic units?

There are many shapes that have 12 sides. For example:

A pyramid with a hendecagon (-sided) base;

a decagonal prism;

a hexagonal dipyramid;

a dodecahedron, and many other shapes.

Without information about what the shape is, and the lengths of its sides, it is impossible to even attempt to answer the question.