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MathGrade 3rd· What Is Perimeter? Measuring Around Shapes

What Is Perimeter? Measuring Around Shapes

Perimeter is the distance all the way around the outside of a shape

Learning Objective

Students will learn what perimeter is and how to measure it by adding up the sides of a shape.

What You'll Learn

  • Perimeter is the distance all the way around the outside of a shape
  • To find perimeter, you add up the length of all the sides
  • A square with 4-inch sides has a perimeter of 4 + 4 + 4 + 4 = 16 inches
  • Perimeter is measured in units like inches, feet, or centimeters
  • You use perimeter in real life — like fencing a yard or framing a picture

Words to Know

Perimeter
The distance all the way around a shape
"The perimeter of the sandbox is 12 feet."
Side
One edge of a shape
"A square has four equal sides."
Inch
A small unit of measurement — width of your thumb
"The side is 5 inches long."

Check What You Learned

Quick Quiz

1 / 5

Which of these is TRUE?

Fun Facts

  • Perimeter is the total distance around the boundary of a 2D shape

    Source: CCSS 3.MD.D.8

  • For a rectangle: P = 2(length + width)

    Source: Mathematics standards

  • For a square: P = 4 x side length

    Source: Mathematics standards

  • For any polygon: P = sum of all side lengths

    Source: Geometry fundamentals

  • The word "perimeter" comes from Greek "peri" (around) + "metron" (measure)

    Source: OED

  • Perimeter is measured in linear units: inches, feet, centimeters

    Source: NCTM

Lesson Info

Grade 3rd
2026-09-10
What Is Perimeter? Measuring Around Shapes

Standards Alignment

Keywords

3rd grade mathmath for kidsperimetermeasuringaroundshapessideinchCCSS.MATH.CONTENT.3.MD.D.8CCSS.MATH.CONTENT.4.MD.A.3kids learningelementary education
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