This unit introduces students to the concept of volume by building on their understanding of area and multiplication.

In grade 3, students learned that the area of a two-dimensional figure is the number of square units that cover it, without gaps or overlaps. Students first found areas by counting squares and began to intuit that area is additive. Later, they recognized the area of a rectangle as a product of its side lengths and found the areas of more-complex figures composed of rectangles.

Here, students learn that the volume of a solid figure is the number of unit cubes that fill it without gaps or overlaps. First, they measure volume by counting unit cubes and observe its additive nature. They also learn that different solid figures can have the same volume.

Next, students shift their focus to right rectangular prisms: building them using unit cubes, analyzing their structure, and finding their volumes. They write numerical expressions to represent their reasoning strategies and work with increasingly abstract representations of prisms.

Later, students generalize that the volume of a rectangular prism can be found by multiplying its side measurements ( ), or by multiplying the area of the base by its height ( ). As they analyze, write, and evaluate different expressions that represent the volume of the same prism, students revisit familiar properties of operations from earlier grades.

Later in the unit, students apply these understandings to find the volume of a solid figure composed of two non-overlapping rectangular prisms and to solve real-world problems involving such figures. In doing so, they also progress from using cubes to using standard units to measure volume.