Maryland Math 3.GR.C.7.c

Math3rd GradeGeometric Reasoning and Measurement

The Standard

Determine the area of composite rectilinear figures by decomposing them into non-overlapping rectangles and adding the areas.

Maryland College and Career Ready Standards for Mathematics (2025) · UNDERSTAND CONCEPTS OF AREA AND PERIMETER.

Teacher's field guide

What Students Need to Do: Students split L-shaped and step-shaped figures into rectangles that do not overlap. They multiply side lengths to find each rectangle’s area, then add the areas in square units.
What Mastery Looks Like: A student can draw a split, label the dimensions of each rectangle, and calculate the total area. They can show that no squares were counted twice or left out.
Common Misconceptions: Some students multiply the full width by the full height and count the empty corner. Others draw overlapping rectangles and count squares twice, or add side lengths instead of finding area.
How to Assess It: On grid paper, draw a 5-by-2 rectangle, then add a 2-by-3 rectangle directly above its left end. Find the total area and show your calculation.

Lesson moves

Build an L shape with square tiles, use different tile colors for two rectangles, and add the tile counts.
Draw two different splits of the same L-shaped grid figure and explain why both give the same area.
Play area match with L-shaped grid cards and answer cards showing two rectangle products and their sum.
Sketch an L-shaped patio from a 6-by-2-foot strip and a 2-by-3-foot strip joined at one end, then calculate its paving area.

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