Circumference Calculator

Free Online Calculation Tool

Circumference Calculator is a free online tool for easily calculating circle circumference from radius or diameter. Using pi (π, approximately 3.14159), it instantly determines accurate circumference length. Useful for math learning, crafts, design, engineering calculations, and various other applications.

Circumference Calculator

Radius (r)

Circumference Formula: C = 2πr

Circumference (C)

Radius (r)

Diameter (d)

Area (A)

Practical Uses for Circumference Calculator

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

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What is Circumference? Basic Knowledge

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Frequently Asked Questions (FAQ)

What is the value of pi (π)?

Pi (π) is approximately 3.14159265358979... Pi is an irrational number with infinitely continuing, non-repeating decimal places. Common calculations use 3.14 or 3.14159, but this tool uses higher precision values.

What's the difference between radius and diameter?

Radius (r) is the distance from the circle's center to any point on the circumference. Diameter (d) is the longest line segment through the center, twice the radius (d = 2r).

How are the circumference formulas derived?

Pi is defined as 'circumference ÷ diameter'. That is, π = C / d. Transforming this equation gives C = πd. Also, since d = 2r, it can also be expressed as C = 2πr.

Why is pi 3.14?

3.14 is an approximate value of pi. The actual π is approximately 3.14159265358979... with infinitely continuing decimals. 3.14 is widely used as a rounded value to simplify calculations.

Are circumference and circle area the same?

No, they are different. Circumference (C) is the perimeter length of a circle, calculated as C = 2πr. Circle area (A) is the space inside the circle, calculated as A = πr². The units also differ (circumference uses length units, area uses length squared units).

What is Earth's circumference?

Earth's equatorial circumference is approximately 40,075km, and polar circumference is approximately 40,008km. Earth is not a perfect sphere but a slightly flattened rotational ellipsoid, making the equatorial circumference longer.

Can you reverse calculate radius from circumference?

Yes, you can. If you know the circumference (C), radius (r) is calculated as r = C / (2π). Diameter (d) is d = C / π.

How many decimal places are accurate?

This tool calculates pi to approximately 15 decimal places. This is sufficient precision for general engineering and scientific calculations. For higher precision calculations, please use specialized numerical computation software.