How to Find the Area of a Circle
Finding the Area of a Circle
The area of a circle is found using the formula:
In this formula, r is the radius of the circle. The image below shows what we mean by radius:
How to Find the Area of a Circle
Finding the area of a circle is easy.
Question
What is the area of a circle with a radius of 5 cm, as shown below?
Step-by-Step:
2
Substitute the radius into the formula. In our example, r = 5.
Area = π × 52 = π × 5 × 5 = 78.5 cm2
Answer:
The area of the circle with a radius of 5 cm is 78.5 cm2.
How to Find the Area of a Circle Using the Diameter
The area of a circle can be found using the diameter rather than the radius.
The area of a circle, using the diameter, is found using the formula:
In the formula, d is the diameter of the circle. The image below shows what we mean by diameter:
Read more about how to find the area of a circle using the diameter
See Also
What is a circle? What is pi? What is the radius? Find the area of a circle using the diameter What is the diameter? Find the area of a circle (
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Interactive Test
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Here's a second test on finding the area of a circle
Here's a third test on finding the area of a circle
Note
What Is a Circle?
A circle is a shape containing a set of points that are all the same distance from a given point, its center.
Radius and Diameter
The diameter of a circle is twice the length of its radius.
If you are given the diameter of a circle, halve it to find the radius and put this in the formula.
Alternatively, use the formula containing diameter.
What Is Pi?
π is the symbol for pi.
π is how many times longer a circle's circumference is than its diameter. It is the circumference divided by the diameter:
π is the same for all circles, and is approximately equal to 3.14.
A Note on Units
The area of a circle is a length times a length, so we say its dimension is length2. (All areas are lengths squared).
This affects the units used. If the radius is in cm, the area is in cm2. If it is in inches, the area is in inches2.