Area and Perimeter

Grade 3 · Math · Study Guide

Learn how to measure the distance around a shape and the space inside it.

Perimeter is the total distance around the outside of a shape. To find the perimeter, you add up all the side lengths. For example, if a rectangle has sides of 4 cm, 6 cm, 4 cm, and 6 cm, the perimeter is 4 + 6 + 4 + 6 = 20 cm.

Area is the amount of space inside a shape. We measure area in square units, like square centimeters (cm²) or square inches (in²). To find the area of a rectangle, you multiply the length by the width. A rectangle that is 4 cm long and 6 cm wide has an area of 4 × 6 = 24 cm².

You can also find area by counting unit squares inside a shape. Each small square on a grid counts as one square unit. Count carefully and you will get the same answer as multiplying.

Remember: perimeter is a length (measured in cm, in, ft) and area is a surface (measured in square units like cm², in², ft²). Always label your answers with the right units so people know what you measured.

Key terms

Perimeter
The total distance around the outside edge of a shape.
Area
The amount of space inside a shape, measured in square units.
Square unit
A unit used to measure area, such as cm² or in².
Length
The measurement of one side of a shape.
Rectangle
A four-sided shape with four right angles and opposite sides that are equal.
Unit square
A square with sides of 1 unit used to measure area by counting.

Flashcards

Perimeter of a rectangle
Add all four sides: length + width + length + width, or (2 × length) + (2 × width).
Area of a rectangle
Length × Width. The answer is always in square units.
Perimeter of a square
4 × side length, because all four sides are equal.
Area of a square
Side × Side (side length squared).
Units for perimeter
Regular length units: cm, in, ft, m — not square units.
Units for area
Square units: cm², in², ft², m².
Counting squares method
Count each unit square inside the shape on a grid to find area.
Difference between area and perimeter
Perimeter goes around the outside; area fills the inside.

Questions

  1. A rectangle has a length of 5 cm and a width of 3 cm. What is its perimeter?

    1. 8 cm
    2. 15 cm
    3. 16 cm
    4. 12 cm
    Show answer

    Answer: 16 cm

    Perimeter = 5 + 3 + 5 + 3 = 16 cm. Add all four sides of the rectangle.

  2. A square has sides of 4 inches each. What is its area?

    1. 8 in²
    2. 12 in²
    3. 16 in²
    4. 20 in²
    Show answer

    Answer: 16 in²

    Area = 4 × 4 = 16 in². Multiply side × side for a square.

  3. Area is measured in square units.

    Show answer

    Answer: True

    Area measures the surface inside a shape, so we always use square units like cm² or in².

  4. A rectangle is 7 cm long and 2 cm wide. Its area is ___ cm².

    Show answer

    Answer: 14

    Area = 7 × 2 = 14 cm².

  5. Which formula gives the area of a rectangle?

    1. Length + Width
    2. Length × Width
    3. Length + Width + Length + Width
    4. Length - Width
    Show answer

    Answer: Length × Width

    Area of a rectangle = Length × Width. The other options describe perimeter or subtraction.

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