Calculate the area of a circle using its radius or diameter. Perfect for geometry problems, design projects, and more.
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Enter Your Measurements
Results
Area
78.54
sq units
Circumference
31.42
units
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Formula
Area = π × r²; Circumference = 2π × r
How to Use This Calculator
How to Use
- 1
Enter the radius of the circle.
- 2
Click calculate to find the area and circumference.
Frequently Asked Questions
Frequently Asked Questions
How do I find the radius from diameter?
Radius is half the diameter. If diameter is 10, radius is 5.
What is π (pi)?
Pi (π) is an irrational number approximately equal to 3.14159. It represents the ratio of a circle's circumference to its diameter.
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About This Calculator
This calculator uses the formula: Area = π × r²; Circumference = 2π × r. All calculations follow industry-standard methods. Results are estimates — always verify with a licensed professional for structural or code-compliant work.
Built and maintained by the CalcSmart team. Last updated March 2026.
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<iframe src="https://calcsmart.io/embed/circle-area-calculator" width="100%" height="520" frameborder="0" style="border-radius:8px;border:1px solid #e5e7eb" title="Circle Area Calculator"></iframe>Free to embed. Attribution link included automatically.