# How To Calculate Circumference of Circle

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How To Calculate Circumference of Circle: Circumference mean enclosing boundary of a close curved, circumference is Latin word which literally means “carrying around”. Circumference of circle means enclosing boundary of a circle. In other geometric figure enclosing boundary known as perimeter. You may familiar with word “perimeter”, it means outline of a geometric figure or you can say that distance around a rectangle, square or triangle is known as perimeter and the distance around a circle is known as circumference. You may need to find out circumference of a circle for some craft projects or math problems for school. There are 3 ways to find out circumference of a circle. To find out circumference of circle you either know radius or area of the circle.

## 1st Way to Calculate Circumference of Circle: When You Know Diameter of Circle

• How to find circumference of circle: There is a simple formula to finding out circumference of a circle using the diameter. Formula of circumference of a circle (C) = πd, where π is pi and “d” is diameter. To find circumference, just multiply diameter of a circle with pi and numerical value of pi (π) is 3.14 or 22/7.
• For example: If diameter of circle is 5 feet then what is circumference of a circle. We can solve this problem with circumference of a circle formula.
• C = πd
• C = 3.14 x 5
• C = 15.7 feet

### Some More Problems: When You Know Diameter of Circle

Problem 1: A gardener wants to fence a circular garden of diameter 21 feet. Find the length of the rope he needs.

Solution 1: For this problem we need to find out circumference of a circle then you get length of the rope he needs.

• C = πd
• C = 3.14 x 21
• C = 65.74 feet

65.74 feet of the rope he needs to fence a circular garden.

Problem 2: You want to put a lace on the edge of a circular table cover whose diameter is 1.5 meter and you want to find length of the lace you required and also want to find out how much it cost you, if one meter of the lace costs \$3.

Solution 2: We need to find out circumference of a circle.

• C = πd
• C = 3.14 x 1.5
• C = 4.71 meter

You required 4.71 meter of the lace.

It will cost you,

• 1/m = \$3
• 4.71 meter = 4.71 x \$3
• Cost of lace = \$14.13

4.71 meter of the lace will cost you \$14.13

## 2nd Way to Calculate Circumference of Circle: When You Know Radius of Circle

• How to find the circumference of a circle: There is easy formula to finding out circumference of a circle using the diameter. Circumference of a circle (C) = 2πr, where π is pi and “r” is radius. Radius is half of diameter, so find out radius = r/2. To find out circumference, multiply radius of circle with pi and numerical value of pi (π) is 3.14 or 22/7.
• For example: If radius of circle is 2 feet then what is circumference of a circle. We can solve this problem with circumference of a circle formula.
• C = 2πr
• C = 2 x 3.14 x 2
• C = 12.56 feet

### Some More Problems: When You Known Radius of Circle

Problem 1: Find the circumference of a circular table-top whose radius is 30 meter.

Solution 1: Formula of circumference of a circle.

• C = 2πr
• C = 2 x 3.14 x 30
• C = 188.4 meter

Circumference of a circular table-top is 188.4 meter.

Problem 2: Let say, you want to put fancy ribbon on edge of circular box and radius of the box is 10 cm. To find the required ribbon, just plug the radius into the formula of circumference of circle.

Solution 2: Formula of circumference of a circle.

• C = 2πr
• C = 2 x 3.14 x 10
• C = 62.8 cm

You will require 62.8 cm of ribbon.

## 3rd Way to Calculate Circumference of Circle: When You Know Area of Circle

• Firstly, you need to find out radius of circle with help to given area of circle. Formula of area of circle is A = πr2, where “A” is area of circle and “r” is radius of circle or pi multiply by radius squared. Using area of circle we can find radius, divide area with pi (π) and then take the square root.
• A = πr2
• A/ π = r2
• √(A/π) = r
• After calculating radius put radius value in formula of circumference of circle. And you can find circumference of circle.
• C = 2πr
• C = 2π √(A/π)
• For example: A circular flower-bed has an area of 1256 yds sq. Find the circumference of the flower-bed.
• A = πr2
• 1256 = 3.14 x r2
• 1256/3.14 = r2
• 400 = r2
• √400 = r
• 20 = r

### Some More Problem: When You Know Area of Circle

Problem: If you want to put a fence around your circular garden and you know that the area of a garden is 2826 yds sq and now you want to know how much fencing you need.

Solution: First we find out radius of circular garden, for that we are using area of circular garden.

• A = πr2
• 2826 = πr2
• 2826 = 3.14 x r2
• 2826/3.14 = r2
• 900 = r2
• √900 = r
• 30 = r

Now we put value of radius in formula of circumference of circle.

• C = 2πr
• C = 2 x 3.14 x 30
• C = 188.4 yds

So, you will need 188.4 yds of fence.