The radius of a circle is 2 kilometers. what is the circles circumference?

Here is the answer to questions like: how to find the area of a circle with diameter 2 km?

Circle Calculator

Use the this circle area calculator below to find the area of a circle given its diameter, or other parameters. To calculate the area, you just need to enter a positive numeric value in one of the 3 fields of the calculator. You can also see at the bottom of the calculator, the step-by-step solution.

Here a three ways to find the area of a circle (formulas):

See below some definitions related to the formulas:

Circumference

Circumference is the linear distance around the circle edge.

Radius

The radius of a circle is any of the line segments from its center to its perimeter. The radius is half the diameter or r = d2.

Diameter

The diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. The diameter is twice the radius or d = 2·r.

The Greek letter π

π represents the number Pi which is defined as the ratio of the circumference of a circle to its diameter or π = Cd . For simplicity, you can use Pi = 3.14 or Pi = 3.1415. Pi is an irrational number. The first 100 digits of Pi are: 3.1415926535 8979323846 2643383279 5028841971 6939937510 5820974944 5923078164 0628620899 8628034825 3421170679 ...

Note:

If you input the radius in centimeters, you will get the answer in square centimeters (cm²), if in inches, will get the answer in square inches (in²) and so on ...

Circumference is often misspelled as circunference.

While every effort is made to ensure the accuracy of the information provided on this website, neither this website nor its authors are responsible for any errors or omissions. Therefore, the contents of this site are not suitable for any use involving risk to health, finances or property.

Does calculating circumference have you running in circles? Our circumference calculator is an easy way for you to find the circumference of any circular object. Simply enter the radius of the circle and hit “calculate.” You can click the “reset” button if you need to clear the circumference calculator in order to find the answer for another circle. 

Try our Circumference Calculator now!

And if you're not sure what the radius is or how to find it, we'll walk you through some of the basics of finding a circle's circumference below.

What is the Circumference of a Circle?

The circumference of a circle is the measurement around a circle's edge. It can be compared to finding the perimeter of a shape (although the word perimeter is reserved specifically for polygons). If you were to cut a circle and lay the outline flat, the length of the line it created would be its circumference. The circumference can be measured in any unit or system that traditionally measures length - imperial (inches, feet, etc.) or metric (centimeters, meters, etc.). Whichever unit the radius is measured in will also be the unit the circumference is calculated in.

The equation used to find circumference is C = 2Πr, where C stands for circumference, R stands for radius, and Π is Pi, a mathematical constant equivalent to approximately 3.14 (see more below).

You can also calculate the circumference of a circle using the diameter, with the equation C = Π * d. If you only have the diameter of a circle and would still like to use this calculator, you can find the radius by dividing the diameter in half.

We suggest working out some problems on your own and using the calculator to check your answer, as it provides you with a solution for each problem but will not show you the work that goes with it.

Parts of a Circle

• Circumference: The distance once around the circle. It can also be understood as the circle's perimeter.
• Radius: The distance from the center of the circle to its edge. No matter which direction you measure in, the radius will be the same from any point on the edge of the circle.
• Diameter: A straight line across the circle that intersects through the center point. This measurement is always equal to twice the radius (2r). 

The Value of Pi

Pi (Π) is a non-terminating number, which means it goes on forever and has no end. Its value is about 3.1415926535897... Pi is also a constant, which means it is always equal to the same value.

The Greek letter p (pronounced as "pie") is used to describe this number. It stands for the ratio between the circumference of any circle and its diameter, and it's true for all circles. This means that any circle’s circumference will be about 3.14 times the length of its diameter.

Circumference Equation Example

What is the circumference of a circle whose radius is 24 inches?

Circumference = 2×Π×r

C = 2 × 3.14 × 24

C = 150.79 inches

When you enter the radius of 24 into our calculator, it provides you with an answer of 150.79644737231007, which is a more precise answer. This is because it uses a more accurate number for Pi, rather than rounding to 3.14.

Our circumference calculator provides circumference of a circle by entering its radius.  Our circumference calculator is free to use any time you want to determine the circumference of a circle!

We also have a fun instructional video on diameter, radius and circumference of a circle right here: Circumference of a Circle Video .

Other Calculators

If you need to solve some geometry exercises, this circumference calculator is the page for you. It is a tool specifically created to find the diameter, circumference and area of any circle. Read on to learn:

• What the definition of circumference is
• How to find the circumference of a circle
• How to convert circumference into diameter

As is the case with all of our tools, the circumference calculator works in all directions - it is also a circumference to diameter calculator, and can be used to convert circumference to radius, circumference to area, radius to circumference, radius to diameter (duh!), radius to area, diameter to circumference, diameter to radius (yes, again with the rocket science), diameter to area, area to circumference, area to diameter or area to radius.

If you want to draw a circle on the Cartesian plane, you might find this equation of a circle calculator useful.

The circumference of a circle is the linear distance of a circle's edge. It is the same as the perimeter of a geometric figure, but the term 'perimeter' is used exclusively for polygons.

Circumference is often misspelled as circumfrence.

The following equation describes the relation between the circumference and the radius R of a circle:

C = 2πR

Where π is a constant approximately equal to 3.14159265...

A similarly simple formula determines the relationship between the area of a circle and its radius:

A = π * R²

1. Determine the radius of a circle. Let's assume it's equal to 14 cm.
2. Substitute this value to the formula for circumference: C = 2 * π * R = 2 * π * 14 = 87.9646 cm.
3. You can also use it to find the area of a circle: A = π * R² = π * 14² = 615.752 cm².
4. Finally, you can find the diameter - it is simply double the radius: D = 2 * R = 2 * 14 = 28 cm.
5. Use our circumference calculator to find the radius when you only have the circumference or area of a circle.

If you wish to calculate the properties of a three-dimensional solid, such as a sphere, cylinder or cone, it's best to use our volume calculator.

You have probably noticed that, since diameter is twice the radius, the proportion between the circumference and the diameter is equal to π:

C/D = 2πR / 2R = π

This proportion (circumference to diameter) is the definition of the constant pi. It is used in many areas, such as physics and mathematics. For example, you can find it in the centrifugal force calculator.

To calculate the circumference, you need the radius of the circle:

1. Multiply the radius by 2 to get the diameter.
2. Multiply the result by π, or 3.14 for an estimation.
3. That's it; you found the circumference of the circle.

Or you can use the circle's diameter:

1. Multiply the diameter by π, or 3.14.
2. The result is the circle's circumference.

The circumference of a circle is the linear distance of the circle's edge. It is equivalent to the perimeter of a geometric shape, although that term perimeter is only used for polygons.

The first person to calculate the Earth's circumference was Eratosthenes, a Greek mathematician, in 240 B.C. He discovered that objects in a city on the Northern Tropic do not throw a shadow at noon on the summer solstice, but they do in a more northerly location. Knowing this, and the distance between the locations, he succeeded in calculating the Earth's circumference.

If you want to find the diameter from the circumference of a circle, follow these steps:

1. Divide the circumference by π, or 3.14 for an estimation.
2. And that's it; you have the circle's diameter.

To find the area of a circle from the circumference, follow these steps:

1. Divide the circumference by π.
2. Divide the result by 2 to get the circle's radius.
3. Multiply the radius by itself to get its square.
4. Multiply the square by π, or 3.14 for an estimation.
5. You found the circle's area from the circumference.

To find the radius from the circumference of a circle, you have to do the following:

1. Divide the circumference by π, or 3.14 for an estimation. The result is the circle's diameter.
2. Divide the diameter by 2.
3. There you go, you found the circle's radius.

• Calculate the circumference as 2 ⨉ radius ⨉ π.
• Calculate the circumference as diameter ⨉ π.
• Wrap a string around the object and measure the length of it.
• Use Omni's circumference calculator.

The formula for the circumference, if the circle's radius is given, is:

Or if the circle's circumference is given:

You can estimate π as 3.14.

To calculate the circumference of a circle with a radius of 1 meter, simply follow these steps:

1. Multiply the radius by 2 to get the diameter of 2 meters.
2. Multiply the result by π, or 3.14 for an estimation.
3. And there you go; the circumference of a circle with a radius of 1 meter is 6.28 meters.

To find the circumference of a cylinder, you have to be aware that a cylinder's cross-section is a circle. If you know the cylinder's radius:

1. Multiply the radius by 2 to get the diameter.
2. Multiply the result by π, or 3.14 for an estimation.
3. That's it; you found the circumference of the cylinder.

Or you can use the cylinder's diameter:

1. Multiply the diameter by π, or 3.14.
2. The result is the cylinder's circumference.

If you want to find the area of a circle with a circumference of 1 meter, do the following:

1. Divide the circumference by π. This is the circle's diameter, in this case, 31.8 centimeters.
2. Divide by 2. This result is the circle's radius of 15.9 centimeters.
3. Multiply the radius with itself, getting the square, in our case 256 cm².
4. Multiply by π, or 3.14 for an estimation.
5. That's it; a circle with a circumference of 1 meter has an area of 795.78 cm².

To find the radius of a circle with a circumference of 10 centimeters, you have to do the following:

1. Divide the circumference by π, or 3.14 for an estimation. The result is the circle's diameter, 3.18 centimeters.
2. Divide the diameter by 2.
3. And there you go, the radius of a circle with a circumference of 10 centimeters is 1.59 centimeters.

Since a circle's circumference is the linear distance of the circle's edge, it describes a length. Therefore, the most common units of a circle's circumference are millimeter, centimeter, meter for the metric system, and inch, feet, and yard for the imperial system.