Radius

usgb/ˈreɪdiəs/
noun

The straight line from the center to the edge of a circle or a ball.

She drew a circle with a radius of 3 centimeters.
Visual representation of "radius" - The straight line from the center to the edge of a circle or a ball

Often appears as...

  • circle's radius
  • sphere radius

Usage tips

Technical

Definition 1 of 4
Visual representation of "radius"
LampPro Tip 1/3

Circle Basics

A radius is essential in geometry for calculating area and circumference of a circle.

Illustration for Circle Basics
Find the area of a circle by using the radius in the formula Area = πr^2.
LampPro Tip 2/3

Measure Twice

Always double-check the length of a radius, as even a small error changes the circle size significantly.

Illustration for Measure Twice
She carefully measured the radius again before cutting the round cake board.
LampPro Tip 3/3

Not a Diameter

Do not confuse radius with diameter; the radius is half the length of the diameter.

Illustration for Not a Diameter
The diameter is twice the radius, so if the radius is 4 cm, the diameter will be 8 cm.
Visual representation of the word "Radius"

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