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Circumference Calculator

Enter any one of the values to calculate the other remaining terms, using the formula C = 2πr when the radius is known or C = πd when the diameter is known.

Note: Just enter only one value to know others.

Radius(R):

cm ▾

Diameter(D):

cm ▾

Circumference(C):

cm ▾

Area(A):

cm² ▾

Related

Circumference of a Circle Calculator

This tool helps you calculate the circumference of a circle, which is the total distance around its edge. By entering just one known value, you can also find the radius, diameter, or area of any circle easily.

If you are solving circle-related geometry problems, this guide simplifies the process for you.

Here’s what you’ll learn:

Definition of circumference and its formula
How to calculate circumference using radius or diameter
How to derive diameter, radius, or area from the circumference

What is the Circumference of a Circle?

The circumference is the distance around the circle’s edge. Think of it like the perimeter of a polygon, but specifically for circular shapes.

what is circumference

🔎 To plot a circle on a Cartesian plane, check our equation of a circle calculator.

Circumference Formulas:

➤ Using Radius

If you know the radius, multiply it by 2 and then by π (pi):

Circumference = 2 × π × r

➤ Using Diameter

If the diameter is given, multiply it directly by π:

Circumference = π × d

➤ Using Area

From the area of a circle, the circumference can be calculated using:

Circumference = 2 × √(π × A)

Where:

r = Radius
d = Diameter
π ≈ 3.14159

How to Calculate the Circumference of a Circle

Using Radius

Measure the radius of the circle.
Multiply the radius by 2.
Multiply the result by π (pi).

Example:

Circle radius = 7 cm

Solution:

2 × 7 = 14

14 × 3.14 ≈ 43.96 cm

Answer: The circumference is 43.96 cm.

Using Diameter

Measure the diameter of the circle.
Multiply it by π (pi).

Example:

Circle diameter = 10 cm

10 × 3.14 ≈ 31.4 cm

Answer: Circumference is 31.4 cm.

🔎 To calculate unknown sides of right triangles, try our Pythagorean theorem calculator.

How to Convert Circumference into Diameter, Radius, or Area

From the circumference (C):

Diameter (D) = C ÷ π
Radius (R) = C ÷ (2 π)
Area (A) = C² ÷ (4 π)

🔎 Explore related calculators: Circumference to Diameter Calculator and Circumcenter Calculator.

FAQs

Is the circumference 3.14 times the diameter?

Yes, because C = πd, and π ≈ 3.14.

How to calculate the radius from the circumference?

Use R = C ÷ (2 π)
Divide the circumference by π to get the diameter
Divide the diameter by 2 to get the radius

Who first calculated the Earth's circumference?

Eratosthenes, a Greek scholar, measured it around 240 B.C. using shadows in Alexandria and Syene.

What is the circumference of a circle with 30 cm diameter?

Use C = πd
C = 3.14 × 30
C ≈ 94.2 cm

What is the circumference of a 60-inch diameter circle?

Multiply diameter by π: 60 × 3.14 ≈ 188.4 inches.

References

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