Area of Irregular Shapes for Grade 3 – Simple Methods & Examples

What Is the Area of an Irregular Shape?

The area of an irregular shape is the space that it occupies, although it does not follow a clean formula. In contrast to the squares or perfect rectangles, irregular shapes have sides that are uneven or their angles don’t line up evenly. That is what makes them tricky in the beginning.

You see irregular shapes everywhere. This can include floor plans, garden plots, or playground markings. Even simple drawings in math books. When students ask, “How do you find the area of an irregular shape?” The answer is rarely one step. It’s about breaking the shape down into parts you already understand.

Once you do that, the problem stops feeling confusing and starts feeling manageable.

Understanding Irregular Shapes with Rectangles and Squares

Irregular shapes become easier once you imagine them as groups of rectangles and squares. This works especially well when you’re dealing with the area of irregular rectangle problems or the area of uneven rectangle layouts.

This is why teachers often introduce the area of irregular rectangle problems using grids. Grids turn strange outlines into familiar blocks. Each block has a clear length and width. That makes the calculation easier.

For example, an uneven rectangle might look confusing as a whole. But split it into two or three regular rectangles, and suddenly you’re just finding simple areas and adding them together. This is also how students slowly understand the area of unequal rectangle shapes without panic.

Key Concepts to Find the Area of Irregular Shapes

• How to break larger area into smaller areas
• Divide the irregular shape into squares and rectangles
• Find the area of each individual squares and rectangles
• Find the area of any irregular shapes

1.1 Area of Square

1. All sides are of equal length in a square.
2. Area of a square = Side x Side
3. Side = 6 inches
4. Area = 6 in x 6 in. = 36 square inches

1.2 Area of Rectangle

As the opposite sides are the same in a rectangle area

Area of the rectangle = Length * Width

Length = 8 inches, Width = 5 inches

Area = 8 in x 5 in = 40 square inches

Jack wants to lay artificial grass for playing golf in the ground. Let us help Jack find the area of the ground to be covered by grass.

Method 1

Draw the figure on the grid paper and count the unit squares covered to find the area.

Total number of squares = 56

Area to be covered by grass = 56 square feet

Method 2

• Break the larger area into smaller parts.
• Look for the possibilities in which the smaller shapes are part of a larger shape.
• Divide the larger area into smaller rectangles and find the area.

The golf area to be covered by grass is divided into rectangles A, B and C

Find individual areas

Area of rectangle A = 4 ft x 3 ft = 12 square feet

Area of rectangle B = 4 ft x 3 ft = 12 square feet

Area of rectangle C = 4 ft x 8 ft = 32 square feet

Total area = 12 + 12 + 32 = 56 square feet

How to Find the Area of an Irregular Shape?

If you’re wondering how to find the area of an irregular shape, follow this process.

• First, divide the shape into smaller rectangles or squares. These should have straight sides and right angles whenever possible.
• Second, measure the length and width of each smaller shape. This step matters. Guessing leads to wrong answers.
• Third, calculate the area of each part using the rectangle formula: Area = length × width.
• Finally, add all the smaller areas together. That total is the area of the full shape.

This method works whether you’re finding the area of uneven rectangle layouts or figuring out how to work out the area of an irregular shape on paper.

Area of Uneven or Unequal Rectangles

Let us understand how to calculate area of uneven rectangle. An uneven or unequal rectangle doesn’t have matching sides. One length may be longer. One width may be shorter. That’s why students often ask how do you calculate the area of an irregular shape.

The rule stays the same. You don’t change the formula. You change how you apply it.

If a rectangle has different lengths on different sides, split it. Treat each section as its own rectangle with clear dimensions. Then calculate each area separately.

This method also explains how to find the area of a rectangle with different lengths. You’re not forcing one formula onto a messy shape. You’re adapting the shape to the formula you already know.

Steps to Find the Area of an Irregular Shape

1. Find all the unknown sides.
2. Divide the irregular shape into squares and rectangles
3. Find the area of each individual squares and rectangles
4. Add all the individual areas to find the total area of the irregular shape.
   Total area = sum of all individual areas

Steps to Find the Area of an Irregular Shape

1. Find all the unknown sides.

In this example, find the values of side a and side b

Side a = 10 – 3 = 7 cm

Side b = 5 – 3 = 2 cm

2. Divide the irregular shape into squares and rectangles

In the example, the figure is divided into one rectangle-A and one square-B 

Total area = Area of Rectangle A + Area of Square B

Steps to find the area of an irregular shape

3. Find the area of each individual squares and rectangles

Area of rectangle A = length x width

= 10 x 2 = 20 square cm

Area of square B = side x side

= 3 x 3 = 9 square cm

4. Add all the individual areas to find the total area of the irregular shape

Total area = Area of rectangle A + Area of rectangle B

= 20 sq. cm + 9 sq. cm

= 29 sq. cm

Solved Examples of Area of Irregular Shapes

Total area of the shaded part = Area of the outer rectangle – Area of the inner rectangle

Area of outer rectangle = 10 cm x 8 cm

= 80 square cm

Area of inner rectangle = 4 cm x 6 cm

= 24 square cm

Total area of shaded part = 80 sq. cm – 24 sq. cm

= 56 square cm

Practice Questions: Find the Area of Irregular Shapes

Find the area of the irregular shapes

Exercise:

Find the area of the shapes shown below.

1.

2.

3.

4.

5.

What We Have Learned About Area

• The area of a surface or a plane figure is the number of square units needed to cover the surface or the figure
• Area of the square =  S x S
• Area of the rectangle  =  Length x Width
• Area is measured using standard units
• To find area of irregular shape
• Break the larger area into smaller parts.
• Look for the possibilities in which smaller shapes are part of the larger shape.
• Divide the larger area into smaller rectangles and find the area.

Summary: Area of Irregular Shapes

To find the area of irregular shapes, the first thing to do is to divid the irregular shape into regular shapes that you can recognize such as triangles, rectangles, circles, squares and so forth.

Then, find the area of these individual shapes and add them up.

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