Saxon Math Grade 3, Section 5: Area Perimeter & Polygon Geometry
In this unit, the year ends with shapes and how to measure them. Your child finds area by covering a shape with squares and by multiplying length by width, finds perimeter by adding side lengths, and sorts polygons, flat shapes with straight sides, into groups. Multiplication from earlier in the year makes the area work quicker.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Section 5?
- Covering shapes with square units to see that area measures the space inside, not the edge. Learn more: Area: how much flat space a shape covers
- Finding the area of rectangles by multiplying, such as a 6-foot by 5-foot rug covering 30 square feet. Learn more: Finding the area of a rectangle
- Adding side lengths to find the perimeter of polygons, and finding a missing side when the total is given. Learn more: Perimeter: the distance around a shape
- Sorting polygons by number of sides and kinds of corners, and naming quadrilaterals like rhombuses and rectangles. Learn more: Sorting four-sided shapes into families
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
You want to cover a rectangular garden with new grass. Which measurement tells you how much grass you need?
- Perimeter
- Length
- Area
How you can help
- Measure a rectangular rug or table in feet, then ask your child for its area by multiplying and its perimeter by adding.
- Ask your child to name the shapes of signs, windows, and tiles on a walk, counting the sides of each polygon.
- Cover a tray or placemat with square crackers, edge to edge with no gaps, and ask your child to count them by rows to find its area.
Where kids can get stuck
- Counting the squares along the edge when the question asks for the space inside.
- Adding a rectangle's length and width only once, so a 6 by 5 rug gets a perimeter of 11 instead of 22.
- Thinking a shape must have equal sides to be a polygon.
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
- area
- The space inside a flat shape, measured in squares.
- perimeter
- The total length of all the sides of a shape.
- polygon
- A flat shape made of straight sides that close up, like a triangle or hexagon.
- quadrilateral
- A flat shape with exactly 4 straight sides and 4 corners.
- square unit
- A square used to measure area, like a square inch or square foot.
- side length
- The measurement of one side of a shape.
- rhombus
- A four-sided shape with all sides equal, like a pushed-over square.
- rectangle
- A four-sided shape whose corners are all square corners.
Ready to build your child’s confidence with area, perimeter, and shapes?
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.
Join the club
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 Saxon Math Grade 3 Section 5 cover?
Saxon Math Grade 3 Section 5 covers these math standards. Each one links to what it means, sample questions, and teaching strategies.
- 3.MD.C.5: Understand area: how many squares it takes to cover a flat shape.
- 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.
- 3.G.A.1: Sort shapes into groups, like quadrilaterals (four-sided shapes).
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.