Volume and Fractional Unit Cubes

A solid or 3-dimensional figure which can be packed without gaps or overlaps using X unit cubes is said to have a volume of X cubic units. For example, if a solid figure or container can hold exactly 5 unit cubes, its volume is said to be 5 cubic units. But what if there are gaps or overlaps? What then? How do we deal with the gaps or overlaps if a 3-dimensional figure or container can’t be filled neatly with unit cubes? Not all 3-dimensional figures can be exactly filled using unit squares. Finding the volume of some figures will require the use of fractional parts of the unit square.