Math Expressions Grade 3, Unit 6: Polygons, Perimeter, and Area
In this unit, your child sorts polygons and quadrilaterals, finds the area of shapes by counting squares and by multiplying, and finds perimeter, the distance around a shape. Children see that two rectangles can have the same perimeter but different areas. It puts the equations from the last unit to work, and the next unit explores fractions.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 6?
- Sorting quadrilaterals by their sides and angles, and seeing that squares, rectangles, and rhombuses all belong to the quadrilateral family. Learn more: Sorting four-sided shapes into families
- Understanding area as the number of square units that cover a shape without gaps or overlaps. Learn more: Area: how much flat space a shape covers
- Finding area by counting square centimeters, square inches, or square feet, and naming the area in square units. Learn more: Finding area by counting squares
- Finding a rectangle's area by multiplying length times width, and splitting L-shaped figures into rectangles to find their area. Learn more: Finding the area of a rectangle
- Finding perimeter, including a missing side length, and comparing rectangles with equal perimeters but different areas. Learn more: Perimeter: the distance around a shape
Sample questions to try together
These are real questions from our practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
Look at the shapes. They are all quadrilaterals. How many of them have 4 square corners?
- 2
- 3
- 1
How you can help
- Measure a rug, a table, or a bed with a tape measure or ruler and ask your child to find both the perimeter and the area.
- Make rectangles with 12 square sticky notes and ask which arrangement has the longest perimeter and which has the shortest, even though the area stays 12.
- Look for quadrilaterals around the home, such as a window, a book cover, and a floor tile, and ask what makes each one a square, rectangle, or rhombus.
Where kids can get stuck
- Adding the length and width to find area, so a 6 by 4 rectangle gets 10 instead of 24.
- Multiplying the sides to find perimeter, so a 5 by 3 rectangle gets 15 instead of 16.
- Writing inches instead of square inches for an area, not yet seeing that area counts squares.
Practice makes perfect
Bobby's Math Club has practice problems that adapt to your child’s level, each with a detailed explanation and an easy-to-follow video, so your child can build confidence in these skills one step at a time.
Words your child will hear
- polygon
- A flat, closed shape with straight sides.
- quadrilateral
- Any flat, closed shape with 4 straight sides.
- perimeter
- The distance all the way around a shape.
- area
- The amount of flat space a shape covers, measured in square units.
- square unit
- The unit for area, such as a square inch or square centimeter.
- length
- How long something is from end to end.
- width
- How wide something is from side to side.
- side length
- How long one side of a shape is.
- rhombus
- A quadrilateral with 4 equal sides.
Ready to build your child’s confidence with area and perimeter?
In Bobby's Math Club, your child practices these skills at just the right level, with a hint when they need one, a clear explanation after every question, and kid-friendly videos. Unlimited practice is free.
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Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.
Which math standards does Math Expressions Grade 3 Unit 6 cover?
Math Expressions Grade 3 Unit 6 covers these math standards. Each one links to what it means, sample questions, and teaching strategies.
- 3.G.A.1: Sort shapes into groups, like quadrilaterals (four-sided shapes).
- 3.MD.C.5: Understand area: how many squares it takes to cover a flat shape.
- 3.MD.C.6: Find the area of a shape by counting squares.
- 3.MD.C.7: Find the area of a rectangle by multiplying its length and width.
- 3.MD.D.8: Find the perimeter, the distance around a shape, or a missing side.
For teachers: Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence. Learn how Bobby's Math Club can help your students grow.