Written by the Fiveable Content Team • Last updated September 2025
Verified for the 2026 exam
Verified for the 2026 exam•Written by the Fiveable Content Team • Last updated September 2025
Definition
The radius is the distance from the center of a circle or sphere to any point on its circumference or surface.
Related terms
Circumference: The circumference is the distance around a circle. It can be calculated using the formula C = 2πr, where r is the radius.
Diameter: The diameter is twice the length of the radius. It is a straight line passing through the center of a circle or sphere and touching two points on its circumference or surface.
Arc Length: Arc length refers to a portion of a curve in a circle's circumference. It can be calculated using θ/360° × 2πr, where θ represents an angle in degrees and r is the radius.