How do you find circle area from diameter?

First find the radius using r = d / 2, then use the formula A = πr².

How do you find circle area from circumference?

First calculate the radius using r = C / (2π), then find the area with A = πr².

What is the difference between radius and diameter?

The radius is the distance from the center of the circle to the edge. The diameter goes across the circle through the center and equals two radii.

Can I enter decimal numbers?

Yes, the calculator supports both integers and decimal values.

What value of π is used?

The calculator uses the standard mathematical value of π with sufficient precision for practical calculations.

Circle Area Calculator

Calculate circle area using radius, diameter, or circumference with step-by-step explanation.

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Enter values

Education

Calculation method

A = πr²

Radius r

Examples

Result

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Enter values and click “Calculate”.

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Circle Area Calculator — How it works

This calculator helps you quickly find the area of a circle in different ways. You can calculate it from radius, from diameter, or from circumference.

Circle area formula

The main formula is:

A = πr²

Here r is the radius of the circle, and π is the mathematical constant approximately equal to 3.14159.

Area from diameter

If the diameter is known, first find the radius:

r = d / 2
A = π(d / 2)²

Area from circumference

If the circumference is known, find the radius like this:

r = C / (2π)

Then use the area formula:

A = πr²

Example calculation

If the radius of the circle is 5, then:

A = π × 5² = π × 25 ≈ 78.5398

What is useful about this calculator

You can enter both whole numbers and decimal values, and the calculator will automatically show the formula, intermediate steps, and final result.

Frequently Asked Questions

How do you find the area of a circle?

The area of a circle is calculated using the formula A = πr².

What is the radius?

The radius is the distance from the center of the circle to its edge.

What is the diameter?

The diameter is a line segment that goes through the center of the circle and equals two radii.

Can you find area from diameter?

Yes, first divide the diameter by 2 to get the radius.

Can you find area from circumference?

Yes, first find the radius using C / (2π), then calculate the area.

Are decimal numbers supported?

Yes, the calculator supports both whole and decimal values.