Math Calculators
Circle Calculator
Find a circle's area, circumference, and diameter.
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Enter details
Result
Area
78.5398
Circumference
31.4159
Diameter
10
About the Circle Calculator
Enter a circle's radius and instantly get its area (πr²), circumference (2πr), and diameter (2r). It's a quick geometry helper for homework, design, and any project involving round shapes — no need to remember which formula uses which constant.
How to use the Circle Calculator
- 1Enter your radius.
- 2Read the result instantly — it recalculates as you type.
- 3Adjust the numbers to model different scenarios.
Frequently asked questions
What is the area of a circle?
Area = π × radius². A circle with radius 5 has an area of about 78.54 square units.
How do I find circumference?
Circumference = 2 × π × radius (or π × diameter). This tool shows both circumference and diameter.