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Instantly calculate circumference and area from radius or diameter

The circumference calculator is a free online tool that automatically calculates circumference and area by simply entering the radius or diameter of a circle. It can be used in various situations such as math homework, architectural and engineering design work, and everyday calculations. It calculates accurately using the formulas C = 2πr (from radius) or C = πd (from diameter).

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Practical Uses for Circumference Calculator

Circumference calculations are widely used from daily life to professional fields:

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What is Circumference? Basic Concepts

Circumference refers to the length of the outer perimeter of a circle. It is the length of the line connecting all points equidistant from the center of the circle.

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Frequently Asked Questions (FAQ)

What's the difference between circumference and perimeter?

Circumference and perimeter mean the same thing. Both refer to the length of the outer boundary line of a circle.

What's the difference between radius and diameter?

Radius is the distance from the center of the circle to the outer edge. Diameter is the longest line segment passing through the center, and is twice the length of the radius (d = 2r).

How accurate is the value of π?

This tool uses JavaScript's Math.PI constant, which has about 15 digits of precision (π ≈ 3.141592653589793). This is sufficient accuracy for general calculations.

Can I reverse calculate the radius from circumference?

Yes, you can. Reversing the formula gives r = C / (2π). For example, if the circumference is 31.42cm, the radius is 31.42 / (2 × 3.14159) ≈ 5cm.

Can I find the radius from the area?

Yes, transforming the area formula A = πr² gives r = √(A/π). If the area is 78.54cm², the radius is √(78.54/3.14159) ≈ 5cm.

What units can I calculate in?

This tool allows you to select various units including cm (centimeters), m (meters), km (kilometers), inch, feet, etc. Results are also displayed in the same unit.

Can I calculate the perimeter of an ellipse?

This tool only calculates circle circumference. Ellipse perimeter requires a different formula and more complex calculations.

How precise are the calculation results?

This tool displays results rounded to 6 decimal places. This is sufficient precision for most practical purposes.