# Area and perimeter

Contents
Area and perimeter help us measure the size of 2D shapes. We’ll start with the area and perimeter of rectangles. From there, we’ll tackle trickier shapes, such as triangles and circles.

## Area and circumference of circles

You already know about area and perimeter of lots of shapes. Now we'll round out those concepts by applying them to circles. Mathematicians call the distance around a circle its circumference and the space inside a circle its area. In this tutorial, we'll learn that there's another type of pi in the math world, and it's even more awesome than apple pie. We'll use pi to find the circumference and area of any circle in the world, no matter how big or how small! Common Core Standards: 7.G.B.4
11:05
Learn how the number Pi allows us to relate the radius, diameter, and circumference of a circle.
2:01
Labeling parts of a circle
Radius, diameter, center, and circumference--all are parts of a circle. Let's go through each and understand how they are defined.
Exercise
Practice finding the radius, diameter, or circumference of a circle. For example, if the diameter of a circle is 16, what is its circumference?
4:02
Area of a circle
In this example, we solve for the area of a circle when given the diameter. If you recall, the diameter is the length of a line that runs across the circle and through the center.
Exercise
Area of a circle
1:53
Circumference of a circle
Here we find the circumference, the distance around a circle, given the area. We're building on our knowledge of the parts of circle.
1:31