Area = 78.5398163397
Circle Calculator
Use this free circle calculator to start from radius, diameter, circumference, or area and find the other circle measurements with steps.
Formula steps Examples included Copy results Private history
Radius5 cm
- Diameter
- 10 cm
- Circumference
- 31.4159265359 cm
- Area
- 78.5398163397 cm^2
Steps
- Start from the known radius.
- Use d = 2r, C = 2pi r, and A = pi r^2.
- The radius is 5 cm.
- The area is 78.5398163397 cm^2.
How to use the circle calculator
- Choose the known circle measurement: radius, diameter, circumference, or area.
- Enter the known value and an optional unit label.
- Press Calculate circle to find radius, diameter, circumference, and area.
- Use examples, recent answers, or copy the result while solving circle problems.
Common uses
Convert radius into diameter, circumference, and area.
Work backward from diameter, circumference, or area.
Check circle formulas for geometry class or quick planning.
Copy circle measurements and formula steps into notes.
Examples
Radius = 5
Radius is about 5
Frequently asked questions
Quick answers about formulas, units, valid measurements, examples, copying, and private in-browser history.
What circle measurements can I start with?
You can start with radius, diameter, circumference, or area. The calculator finds the remaining circle measurements.
What formulas does the Circle Calculator use?
It uses d = 2r, C = 2pi r, and A = pi r^2. It rearranges those formulas when you start from diameter, circumference, or area.
What is the difference between radius and diameter?
Radius is the distance from the center to the circle edge. Diameter is the full distance across the circle through the center, so diameter is twice the radius.
Can I enter area to find radius?
Yes. Area mode uses r = sqrt(A / pi) to work backward from a known area.
Should I use Area Calculator instead?
Use Circle Calculator when you want all circle measurements. Use Area Calculator when you only need area for one of several common shapes.
Is my circle history private?
Yes. Recent circle answers stay only in the current browser tab while you use the page. They are not sent to a server.