A circle’s radius is the distance from its center to any point on the circle, while its diameter is a segment joining two points on the circle that passes through the center. Because a diameter consists of two radii, their lengths satisfy and , across diagrams and measurement units; this relationship supports later work with circumference and area without involving more advanced circle theorems.
The radius is the distance from the center of a circle to its edge. The diameter goes all the way across the circle through its center.
A diameter is made of two equal radii, so:
To find the radius from a diameter, divide by :
Example: A circle has a radius of . What is its diameter?
Use the relationship .
Substitute :
Multiply:
The diameter is .
Click a topic below to practice the foundational skills you'll need, learn the steps, or master this skill
Earned ?