How To Solve A Circle

How You Can Find The Area Of A Circle

Circles are a very interesting part of the geometry. The only thing you need to solve one (to find anything about it) is the length of its radius. This is completely enough to find a circle's area, circumference and diameter. In other words, radius is totally enough to define a circle. After you have it, you can use the following formulas to solve any circle. But firs, let's define some basic things as follows:

C - circumference
r - radius
d - diameter
pi - 3.14159 - mathematical constant
* - the sign for multiplication

How to find the area

To calculate the area, you have to use the following formula:

Area = pi * r2

Example: to find the area of a circle with radius 2 cm., we have to make the following calculation: 2 x 3.14 x 2 x 2 = 12.56 cm2.

How to find the circumference

The circumference of a circle can be calculated with the following formula:

C = 2*pi*r

Example: if we have a circle with a radius of 2 cm., its circumference is: 2 * 3.14 * 2 = 12.56 cm

Please Note
The mathmatical constant pi is is approximately equal to 3.14159. This number has infinite numbers after the coma, so its decimal representation never ends. This is why nobody can calculate exactly the area and the circumference of a circle...

Circle Solver / Calculator


How to use the calculator

This is a simple tool, with which you can find everything about a certain circle. For this purpose, you need to know one of the specified things about it: diameter (radius); area; circumference. Just enter one of these measures and click the button after its field. Thia way all other measures will be calculated...

This is a very convenient tool, if you already know how to make these calculations and this has become a boring task for you. If you are new to calculating circles, you'd better do this manually to understand things better.

Circle Defined By 3 Poins - Solver

Any circle can be completely defined with only three points if, and only if, they are not on the same line. That means if we have three points meeting this condition, there is only one circle (with a specific raius), that can be drawn. This tool can find the circle passing through any three points on the Cartesian plane. For this purpose, you need to enter the coordinates of the points in this format: x1,y1 and pres the button below.

Enter three points {x, y}:
x y
Center and radius:
Xo =
Yo =
radius =

Find more info about this widget here:

How To Find The Area Of A Circle - Video

Here is a nice and short video about finding the area of a circle. After watching it, you will gain some knowledge and this task will not be a problem for you anymore. So if it's difficult for you to understand this process, watch this movie now: