Lesson objective: Understand that a cube with side length 1 unit is called a unit cube and measures volume.

Students bring prior knowledge of unit squares from 3.MD.5. This prior knowledge is extended to volume as students discover what unit is used to measure volume in three-dimensional figures. A conceptual challenge students may encounter is understanding how sometimes we use the term unit cubes, while other times we replace the word "unit" with an actual unit of measurement such as inches or feet.

The concept is developed through work with a rectangular shoebox, which the students can determine is being packed with unit cubes or not unit cubes.

This work helps students deepen their understanding of equivalence because it allows them to explore a new unit of measurement and reason about “packing” volume, which is more difficult than iterating a unit to measure length and measuring area by tiling. Students learn about a unit of volume, such as a cube with a side length of 1 unit, called a unit cube.

Students engage in Mathematical Practice 3 (construct viable arguments) as students choose whether dominoes or dice are cubes, then convince someone who is in opposition.

**Key vocabulary:**

- cube
- unit cube
- cubic units
- inch cubes
- cubic inches
- centimeter cubes
- cubic centimeters
- unit square
- volume

**Special materials needed:**

- unit cubes