What Is Volume?

See volume as the space inside a solid, counted in cubes that leave no gaps or overlaps.

Warm-up, learn, try it together, practice, then a quick check. About 15 minutes.

What children learn in Level 1

Welcome to the Cube Warehouse! Everything here gets packed in boxes. You already know length, which measures a line, and area, which covers a flat surface. Now we'll measure a third thing.
Volume is the amount of space inside a solid. A box has volume because it has space to fill. A flat square doesn't have any.
We measure volume with unit cubes. A unit cube has sides that are each 1 unit long, so its volume is 1 cubic unit.
Pack cubes in a box with no gaps and no overlaps. Gaps would leave space uncounted, and overlaps would count the same space twice. This box holds 8 cubes, so its volume is 8 cubic units.

Georgia's K-12 Mathematics Standards:

5.GSR.8.3 — Investigate volume of right rectangular prisms by packing them with unit cubes without gaps or overlaps. Then, determine the total volume to solve problems.