The diameter of a circle is the length of the line through the center and touching two points on its edge. In the figure above, drag the orange dots around and see that the diameter never changes.
Sometimes the word 'diameter' is used to refer to the line itself. In that sense you may see "draw a diameter of the circle". In the more recent sense, it is the length of the line, and so is referred to as "the diameter of the circle is 3.4 centimeters"
The diameter is also a chord. A chord is a line that joins any two points on a circle. A diameter is a chord that runs through the center point of the circle. It is the longest possible chord of any circle.
The center of a circle is the midpoint of its diameter. That is, it divides it into two equal parts, each of which is a radius of the circle. The radius is half the diameter.
|ENTER ANY ONE VALUE|
Use the calculator above to calculate the properties of a circle.
Enter any single value and the other three will be calculated. For example: enter the diameter and press 'Calculate'. The area, radius and circumference will be calculated.
Similarly, if you enter the area, the radius needed to get that area will be calculated, along with the diameter and circumference.
The radius is the distance from the center to any point on the edge.
As you can see from the figure above, the diameter is two radius lines back to back,
so the diameter is always two times the radius.
See radius of a circle
Circumference The circumference is the distance around the edge of the circle. See Circumference of a Circle for more.