What is the difference between a radius and diameter?

A radius and a diameter are both measurements associated with circles, but they have different meanings and measurements:

Radius:

The radius of a circle is the distance from the center of the circle to any point on its circumference (outer edge).
It is half the length of the diameter.
The symbol typically used to represent the radius is "r."
Diameter:

The diameter of a circle is the distance across the circle, passing through its center and touching two points on the circumference.
It is equal to twice the length of the radius.
The symbol typically used to represent the diameter is "d."
In mathematical terms, you can relate the radius (r) and diameter (d) of a circle with the following equation:

d = 2r

So, the diameter is always twice as long as the radius. These measurements are fundamental when working with circles and are used in various geometric calculations, such as finding the circumference, area, or other properties of a circle.