The radius is the distance from the center of a circle to its edge. Because the diameter spans the circle through the center, the radius is exactly one half of the diameter.
⚠This calculator uses diameter as the input. Diameter must be zero or positive.
How Radius Works
Radius controls the size of a circle and appears in almost every circle formula, including area, circumference, arcs, and sectors.
Center to Edge
Radius starts at the center.
Half Diameter
r equals d divided by 2.
Circle Size
Larger radius means larger circle.
Formula Base
Area and circumference both use radius.
💡 Example: If d=14, r=14/2=7.
Applications of Radius
Circle AreaCircumferenceArc LengthEngineering Design
Frequently Asked Questions
What is a radius calculator?▼
It calculates circle radius from diameter.
What is the radius formula?▼
From diameter, the formula is r=d/2.
How do I use this calculator?▼
Enter the diameter and click Calculate to get the radius.
Can radius be negative?▼
No. Radius is a distance and cannot be negative.
Where is radius used?▼
Radius is used in circle area, circumference, arcs, sectors, and circular design.
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