The diameter of a circle is the distance straight across it through the center. It is twice the radius, and it is the longest chord any circle has.
Math Dictionary / Diameter
Diameter
The diameter is a line segment that passes through the center of a circle and touches both sides.
GeometryGrade 6Grade 7Grade 8GEDSATACT
What it means
The diameter is twice the radius.
Also called: across a circle
Examples
| If radius = 4, diameter = 8 |
| The diameter cuts a circle in half |
| d = 2r |
Common mistake
The diameter must pass through the center of the circle.
Try one
Question: If a circle has radius 7, what is its diameter?
Show answer
14.