Radius Of A Circle

All math tools

Calculate the radius of a circle from its area, circumference, or diameter.

Input Parameters

Property Provided

Input Value

Calculated Radius

5.0000units

Radius (r)

Derived distance from center to edge

Diameter10.00

Circumference31.42

About this calculator

Quick Reference

π (Pi)≈ 3.14159

Relationshipd = 2r

Circle Sum360°

Understanding the Radius

The radius of a circle is the distance from the center to any point on its boundary. It is the most fundamental property of a circle, as all other measurements (diameter, circumference, area) are direct functions of the radius. In geometry, the radius is also half the length of the diameter.

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Pro Tips

Units: If your area is in square cm, your radius will be in cm.
Precision: Always use a precise value of π (3.14159...) for engineering calculations.
Scale: Doubling the radius quadruples the area (Area ∝ r²).

Fun Facts

"The word 'radius' comes from the Latin 'radius', meaning 'spoke' of a wheel."
"The plural of radius is 'radii'."
"Archimedes was one of the first to rigorously calculate circle properties using polygons."

Formula: r = d/2 = C/(2π) = √(A/π)