Math Dictionary / Radius
Radius
The radius is a line segment from the center of a circle to any point on the circle.
GeometryGrade 6Grade 7Grade 8GEDSATACT
What it means
The radius is half the diameter.
Also called: r
Examples
| If diameter = 10, radius = 5 |
| All radii in the same circle have equal length |
| Circle area uses r^2 |
Common mistake
The radius starts at the center, not at one side of the circle.
Try one
Question: If a circle has diameter 18, what is its radius?
Show answer
9.