TOPIC 9 · GRADES 3–4 FOUNDATION

Area, Perimeter, and Composite Shapes

Separate the space inside a figure from the distance around it.

MA.3.GR.2.1–2.4 · MA.4.GR.2.1–2.2

BIG IDEA

Area counts square units covering a surface; perimeter adds linear units around the boundary. Equal areas can have different perimeters and vice versa.

WHAT TO KNOW

For a rectangle, area = length × width and perimeter = 2 × length + 2 × width.
Unit squares must cover an area without gaps or overlaps.
Composite rectilinear shapes can be split into non-overlapping rectangles, then recombined.

WATCH OUT

Square units belong to area; ordinary length units belong to perimeter.

TRY IT

Resize a rectangle and compare how its area and perimeter change.

Choose the next topic from the lesson rail when you are ready.