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Lesson 26: Introduction to Area and Perimeter
The concepts of area and perimeter come up again and again in math, and also in everyday life. They are very useful terms to know, and are easy to understand.
Don't forget to watch the embedded video clip for this lesson at the bottom of the page. Please be sure to read the embedded video information and disclaimer.
The definitions of area and perimeter
need to be memorized. The perimeter is the distance around a shape.
Take a look at
the rectangle at right.
The length is 6 cm., and the width is 2 cm. To find the perimeter
of the rectangle, we just add up the distance around
the shape. Even though only two of the sides are labeled, we know
what the other two sides measure, since we know how a rectangle works.
It has two lengths and two widths. To find the perimeter, all we
have do is add 6+6+2+2, to get 16 cm., which is our answer.
This works for unusual shapes as well, although we would probably need to know the measurements of all the sides, unless we could somehow figure it out. No matter what the shape, and no matter how many sides it has, just add up the measurements of the lengths of each side to find the perimeter.
The area of a shape is calculated by multiplying its length times its width. For now, you will only work with simple shapes like squares and rectangles. Later you'll learn how to find the area of more complicated or unusual shapes.
Let's look at another rectangle, pictured below. To find the area, we just multiply the length times width. In this case, we'll multiply 7 x 3, to get 21. However, it's incorrect to say that the answer is just 21, or even 21 cm.. When calculating the area, we're not concerned about the distance around the shape, we're concerned about how much space is inside the shape. The proper answer is 21 cm2, which is read as "21 centimeters squared." Later you'll learn more about why we write the answer like that, but for now, understand that what we are actually measuring is how many squares can fit inside the shape. From the picture, you can see that since the length of the rectangle is 7 cm, and the width is 3 cm, we can fit 21 squares inside the shape, each one measuring 1cm x 1cm. That's why we say that the area is 21 cm squared, or sometimes 21 square cm.
For now, just remember that the perimeter of a shape is the sum of its sides, and the area is the length times the width. Later you will learn more.
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