What is the formula for the area of a circle?

The area formula is `A = π × r²`, where `r` is radius and `π ≈ 3.14159265`.

What is the formula for the circumference of a circle?

The circumference formula is `C = 2 × π × r` or `C = π × D`, where `D` is diameter.

How do you find the radius from the circumference?

Divide circumference by 2π: `r = C / (2π)`.

How do you find radius from circle area?

Take the square root of area divided by π: `r = √(A / π)`.

What is the relationship between radius and diameter?

Diameter is exactly twice the radius (`D = 2r`), passing straight through the center point of the circle from one edge to the opposite edge.

How do I calculate circle area from circumference?

Use the formula: `Area = C² / (4π)`, where C is the circumference and π is approximately 3.14159.

Math & Statistics Cluster

Circle Calculator (Area, Circumference, Radius & Diameter)

Calculate circle area, circumference, radius, and diameter from any single known dimension.

TL;DR: Circle Calculator computes all geometric properties of a circle (Area $A = \pi r^2$, Circumference $C = 2\pi r$, Diameter $D = 2r$) from any single input.

Radius

What Are the Core Geometric Formulas for a Circle?

The fundamental circle formulas are: Radius = r; Diameter D = 2r; Circumference C = 2πr = πD; Area A = πr² = (π/4)D². Given any one of these four measurements, all other values can be derived using π ≈ 3.14159265.

How to Use the Circle Calculator

Our Circle Calculator performs high-precision mathematical operations directly in your browser with zero latency and complete client-side privacy.

Select your known circle dimension: Radius, Diameter, Circumference, or Area.
Enter the numerical measurement value.
Click 'Calculate Circle' to solve for all remaining geometric properties.
Review the step-by-step formula derivations and exact π multiples.
Copy the calculated measurements in metric or imperial units.

Mathematical Formula & Equations

Calculates area, circumference, diameter, radius, and spherical volume from any single circular dimension.

\[ A = \pi r^2 = \frac{\pi d^2}{4}, \quad C = 2\pi r = \pi d \]

Calculation Example

For a circle with radius $r = 7\text{ cm}$: $$\text{Area } A = \pi (7^2) = 49\pi \approx 153.94\text{ cm}^2, \quad \text{Circumference } C = 2\pi(7) \approx 43.98\text{ cm}$$

100% Client-Side Privacy & Data Security

All calculations, amortization schedules, variables, and sensitive numerical datasets execute 100% locally in your web browser memory. Your financial, medical, and personal values are never transmitted, logged, or uploaded to any external server.

Frequently Asked Questions

: The area formula is `A = π × r²`, where `r` is radius and `π ≈ 3.14159265`.
: The circumference formula is `C = 2 × π × r` or `C = π × D`, where `D` is diameter.
: Divide circumference by 2π: `r = C / (2π)`.
: Take the square root of area divided by π: `r = √(A / π)`.
: Diameter is exactly twice the radius (`D = 2r`), passing straight through the center point of the circle from one edge to the opposite edge.
: Use the formula: `Area = C² / (4π)`, where C is the circumference and π is approximately 3.14159.

Cite This Calculator

Need to reference this online calculator in a financial proposal, academic paper, blog post, or classroom curriculum? Copy a citation below.

NexLove.org. (2026). Circle Calculator [Online Calculation Tool]. https://nexlove.org/tools/circle-calculator

“Circle Calculator.” NexLove.org, 2026, nexlove.org/tools/circle-calculator.

NexLove.org (2026) Circle Calculator. Available at: https://nexlove.org/tools/circle-calculator (Accessed: 2026).

@misc{nexlove_circle_calculator,
  title = {Circle Calculator},
  author = {{NexLove.org}},
  year = {2026},
  url = {https://nexlove.org/tools/circle-calculator}
}

Embed This Tool

Add the live Circle Calculator to your own website with this snippet — it loads the real, working calculator in an iframe.

<iframe src="https://nexlove.org/embed/circle-calculator.html" width="100%" height="600" style="border:1px solid #e2e8f0;border-radius:12px" title="Circle Calculator — NexLove.org" loading="lazy"></iframe>

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