Circle Radius Calculator
Calculate radius from area, circumference, or diameter and get all circle properties
Calculate Radius
Enter the area in square units
Visualization
Formulas
Radius from Area:
r = √(A/π)
where A is the area
Radius from Circumference:
r = C/(2π)
where C is the circumference
Radius from Diameter:
r = d/2
where d is the diameter
Other Circle Properties:
- Diameter: d = 2r
- Circumference: C = 2πr
- Area: A = πr²
Calculation History
Frequently Asked Questions
What is the radius of a circle?
The radius is the distance from the center of a circle to any point on its edge. It's exactly half of the diameter and is one of the fundamental measurements of a circle. All radii of a circle are equal in length.
How do you find radius from area?
To find the radius from area, use the formula r = √(A/π). First divide the area by pi (approximately 3.14159), then take the square root of the result. For example, if the area is 100, the radius would be √(100/π) ≈ 5.64 units.
How do you find radius from circumference?
To find the radius from circumference, use the formula r = C/(2π). Divide the circumference by 2π (approximately 6.28318). For example, if the circumference is 31.4, the radius would be 31.4/(2π) ≈ 5 units.
Why is knowing the radius important?
The radius is crucial for calculating all other circle properties. It's used in engineering for wheel design, in architecture for circular structures, in astronomy for planetary calculations, in manufacturing for circular parts, and in countless everyday applications like pizza sizing and pool dimensions.
What Users Say
"Exactly what I needed for reverse engineering circular parts. Input the area from blueprints and instantly get the radius. Brilliant!"
Alex K.
Product Designer
"Great teaching tool! Helps students understand the inverse relationship between radius and other circle measurements."
Dr. Rachel S.
University Professor
"Perfect for my pool installation business. Customers give me area requirements and I can quickly determine the radius needed."
Frank D.
Pool Contractor
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