How do we find the circumference when the radius is given? (<im a lil confuse)

if the *diameter* is given we find the circumference by diameter x pi, so if the radius is half the value of the diameter then if you are only given the *radius* we find the circumference by radius x 2 x pi because radius x 2 = diameter

can you tell me the drivation of this formula

Here the Greek letter π represents a constant, approximately equal to 3.14159, which is equal to the ratio of the circumference of any circle to its diameter. One method of deriving this formula, which originated with Archimedes, involves viewing the circle as the limit of a sequence of regular polygons.

what happens if the circle is not perfectly round?

Then technically it's not a circle

What is zero divided by zero

Interesting question! Think of 0 divided by 0 as the answer to the question “what number times 0 is 0?”. Because any number times 0 is 0, 0 divided by 0 can be anything! For this reason, 0 divided by 0 is called indeterminate. If you take calculus later on, you will frequently encounter the indeterminate expression 0 divided by 0 in limit problems. What this means is that the result is inconclusive, so more work is required to calculate the limit or determine that the limit doesn’t exist.

i have a question why do you need to know this

If you are asking why you need to know math, let me explain: How are you going to get a job? {Let me give you an example: My brother joined the Army a few months ago, but before he joined he had to take the ASVAB a test mostly on math skills which determines the job you will get-do you want to be a toilet-cleaner or a soldier?-} You may not join the Army but in life you have to face what you may not like. Math may not be your favorite, but just do your best! YOU CAN DO IT! Have a BLESSED day! M.L.M.

Do you guys like to answer in terms of pi or do you guys like to get the answer in a decimal?

If you are using that value for another calculation, it's better to leave it in exact form (like you said, in terms of pi). Otherwise, probably show the answer as a decimal to a certain amount after putting it in the calculator. You don't want to round an answer that's used for further calculations as you lose some well-needed precision.

How to I find the diameter of a circle when the circumference is given?

Just divide the circumference by pi or 3.14.

how do i find the circumference if the diameter is given

Hi, to find the circumference and you have the diameter all you have to do is do the diameter times pi and the answer you get is the circumference. Another formula to find the circumference is if you have the diameter you divide the diameter by 2 and you get the radius. Once you have the radius you times the radius by 2 and times it by pie and then you get the circumference. Here are the two different formulas for finding the circumference: C = πd C = 2πr d = diameter, C = circumference, and r = radius Hope this helped :)

Main content

Radius, diameter, & circumference

Q: How do we find the circumference when the radius is given? (<im a lil confuse)

if the *diameter* is given we find the circumference by diameter x pi, so if the radius is half the value of the diameter then if you are only given the *radius* we find the circumference by radius x 2 x pi because radius x 2 = diameter

Q: can you tell me the drivation of this formula

Here the Greek letter π represents a constant, approximately equal to 3.14159, which is equal to the ratio of the circumference of any circle to its diameter. One method of deriving this formula, which originated with Archimedes, involves viewing the circle as the limit of a sequence of regular polygons.

Q: what happens if the circle is not perfectly round?

Then technically it's not a circle

Q: What is zero divided by zero

Interesting question! Think of 0 divided by 0 as the answer to the question “what number times 0 is 0?”. Because any number times 0 is 0, 0 divided by 0 can be anything! For this reason, 0 divided by 0 is called indeterminate. If you take calculus later on, you will frequently encounter the indeterminate expression 0 divided by 0 in limit problems. What this means is that the result is inconclusive, so more work is required to calculate the limit or determine that the limit doesn’t exist.

Q: i have a question why do you need to know this

If you are asking why you need to know math, let me explain: How are you going to get a job? {Let me give you an example: My brother joined the Army a few months ago, but before he joined he had to take the ASVAB a test mostly on math skills which determines the job you will get-do you want to be a toilet-cleaner or a soldier?-} You may not join the Army but in life you have to face what you may not like. Math may not be your favorite, but just do your best! YOU CAN DO IT! Have a BLESSED day! M.L.M.

Q: Do you guys like to answer in terms of pi or do you guys like to get the answer in a decimal?

If you are using that value for another calculation, it's better to leave it in exact form (like you said, in terms of pi). Otherwise, probably show the answer as a decimal to a certain amount after putting it in the calculator. You don't want to round an answer that's used for further calculations as you lose some well-needed precision.

Q: How to I find the diameter of a circle when the circumference is given?

Just divide the circumference by pi or 3.14.

Q: how do i find the circumference if the diameter is given

Hi, to find the circumference and you have the diameter all you have to do is do the diameter times pi and the answer you get is the circumference. Another formula to find the circumference is if you have the diameter you divide the diameter by 2 and you get the radius. Once you have the radius you times the radius by 2 and times it by pie and then you get the circumference. Here are the two different formulas for finding the circumference: C = πd C = 2πr d = diameter, C = circumference, and r = radius Hope this helped :)

Google Classroom

Learn the relationship between the radius, diameter, and circumference of a circle.

What is a circle?

We've all seen circles before. They have this perfectly round shape, which makes them perfect for hoola-hooping!

Every circle has a center, which is a point that lies exactly at the... well... center of the circle. A circle is a shape where distance from the center to the edge of the circle is always the same:

You might have suspected this before, but in fact, the distance from the center of a circle to any point on the circle itself is exactly the same.

Radius of a circle

This distance is called the radius of the circle.

Which of the segments in the circle below is a radius?

Diameter of a circle

The diameter is the length of the line through the center that touches two points on the edge of the circle.

Which of the segments in the circle below is a diameter?

Notice that a diameter is really just made up of two radii (by the way, "radii" is just the plural form of radius):

So, the diameter

d

of a circle is twice the radius

r

$d = 2 r$ ‍

Find the diameter of the circle shown below.

units

Find the radius of the circle shown below.

units

Circumference of a circle

The circumference is the distance around a circle (its perimeter!):

Here are two circles with their circumference and diameter labeled:

Let's look at the ratio of the circumference to diameter of each circle:

	Circle 1	Circle 2
$\frac{Circumference}{Diameter}$ ‍:	$\frac{3.14159 …}{1} = 3.14159 …$ ‍	$\frac{6.28318 …}{2} = 3.14159 …$ ‍

Fascinating! The ratio of the circumference

C

to diameter

d

of both circles is

3.14159 …

$\frac{C}{d} = 3.14159 …$ ‍

This turns out to be true for all circles, which makes the number

3.14159 …

one of the most important numbers in all of math! We call the number pi (pronounced like the dessert!) and give it its own symbol

π

$\frac{C}{d} = π$ ‍

Multiplying both sides of the formula by

d

gives us

$C = π d$ ‍

which lets us find the circumference

C

of any circle as long as we know the diameter

d

Using the formula $C = π d$ ‍

Let's find the circumference of the following circle:

The diameter is

10

, so we can plug

d = 10

into the formula

C = π d

$C = π d$ ‍

$C = π \cdot 10$ ‍

$C = 10 π$ ‍

That's it! We can just leave our answer like that in terms of

π

. So, the circumference of the circle is

10 π

units.

Your turn to give it a try!

Find the circumference of the circle shown below.
Enter an exact answer in terms of $π$ ‍.

units

Challenge problem

Find the arc length of the semicircle.
Enter an exact answer in terms of $π$ ‍.

units

Want to join the conversation?

Sort by:

Wirdatul Marsya
Posted 6 years ago. Direct link to Wirdatul Marsya's post “How do we find the circum...”
How do we find the circumference when the radius is given? (<im a lil confuse)
Button navigates to signup pageComment on Wirdatul Marsya's post “How do we find the circum...”
(116 votes)
Answer
- joycezhang99
  Posted 5 years ago. Direct link to joycezhang99's post “if the *diameter* is give...”
  if the diameter is given we find the circumference by diameter x pi, so if the radius is half the value of the diameter then if you are only given the radius we find the circumference by radius x 2 x pi because radius x 2 = diameter
  Comment on joycezhang99's post “if the *diameter* is give...”
  (119 votes)
Blake Terryberry
Posted 3 years ago. Direct link to Blake Terryberry's post “what happens if the circl...”
what happens if the circle is not perfectly round?
Button navigates to signup pageComment on Blake Terryberry's post “what happens if the circl...”
(13 votes)
Answer
- pao
  Posted 2 years ago. Direct link to pao's post “Then technically it's not...”
  Then technically it's not a circle
  Comment on pao's post “Then technically it's not...”
  (60 votes)
KalebS
Posted a year ago. Direct link to KalebS's post “chicken sandwich”
chicken sandwich
Button navigates to signup pageComment on KalebS's post “chicken sandwich”
(34 votes)
Answer
- Jordan, Jared
  Posted 8 months ago. Direct link to Jordan, Jared's post “chicken sandwich”
  chicken sandwich
  Comment on Jordan, Jared's post “chicken sandwich”
  (6 votes)
Robin
Posted 5 years ago. Direct link to Robin's post “can you tell me the driva...”
can you tell me the drivation of this formula
Button navigates to signup pageComment on Robin's post “can you tell me the driva...”
(16 votes)
Answer
- ibrahim amir
  Posted 5 years ago. Direct link to ibrahim amir's post “Here the Greek letter π r...”
  Here the Greek letter π represents a constant, approximately equal to 3.14159, which is equal to the ratio of the circumference of any circle to its diameter. One method of deriving this formula, which originated with Archimedes, involves viewing the circle as the limit of a sequence of regular polygons.
  Comment on ibrahim amir's post “Here the Greek letter π r...”
  (40 votes)
je.avina27
Posted 2 years ago. Direct link to je.avina27's post “why is this so hard :(”
why is this so hard :(
Button navigates to signup pageComment on je.avina27's post “why is this so hard :(”
(21 votes)
Answer
- oliverw44
  Posted a year ago. Direct link to oliverw44's post “fr bro”
  fr bro
  Comment on oliverw44's post “fr bro”
  (7 votes)
BiShOP
Posted 3 years ago. Direct link to BiShOP's post “how do i find the circumf...”
how do i find the circumference if the diameter is given
Button navigates to signup pageComment on BiShOP's post “how do i find the circumf...”
(1 vote)
Answer
- 𝓛𝓪𝓴𝓼𝓱𝓲 🌺
  Posted 3 years ago. Direct link to 𝓛𝓪𝓴𝓼𝓱𝓲 🌺's post “Hi, to find the circumfer...”
  Hi, to find the circumference and you have the diameter all you have to do is do the diameter times pi and the answer you get is the circumference. Another formula to find the circumference is if you have the diameter you divide the diameter by 2 and you get the radius. Once you have the radius you times the radius by 2 and times it by pie and then you get the circumference. Here are the two different formulas for finding the circumference:
  C = πd
  C = 2πr
  d = diameter, C = circumference, and r = radius
  Hope this helped :)
  Comment on 𝓛𝓪𝓴𝓼𝓱𝓲 🌺's post “Hi, to find the circumfer...”
  (33 votes)
Nathan Kittinger
Posted a year ago. Direct link to Nathan Kittinger's post “What is zero divided by z...”
What is zero divided by zero
Button navigates to signup pageComment on Nathan Kittinger's post “What is zero divided by z...”
(9 votes)
Answer
- Ian Pulizzotto
  Posted a year ago. Direct link to Ian Pulizzotto's post “Interesting question! Th...”
  Interesting question! Think of 0 divided by 0 as the answer to the question “what number times 0 is 0?”. Because any number times 0 is 0, 0 divided by 0 can be anything! For this reason, 0 divided by 0 is called indeterminate.
  
  If you take calculus later on, you will frequently encounter the indeterminate expression 0 divided by 0 in limit problems. What this means is that the result is inconclusive, so more work is required to calculate the limit or determine that the limit doesn’t exist.
  Comment on Ian Pulizzotto's post “Interesting question! Th...”
  (12 votes)
edie marcos
Posted 7 months ago. Direct link to edie marcos's post “i have a question why do ...”
i have a question why do you need to know this
Button navigates to signup pageComment on edie marcos's post “i have a question why do ...”
(8 votes)
Answer
- Marissa.L.Medina
  Posted 7 months ago. Direct link to Marissa.L.Medina's post “If you are asking why you...”
  If you are asking why you need to know math, let me explain:
  How are you going to get a job?
  {Let me give you an example: My brother joined the Army a few months ago, but before he joined he had to take the ASVAB a test mostly on math skills which determines the job you will get-do you want to be a toilet-cleaner or a soldier?-}
  You may not join the Army but in life you have to face what you may not like.
  Math may not be your favorite, but just do your best!
  YOU CAN DO IT!
  Have a BLESSED day!
  M.L.M.
  Comment on Marissa.L.Medina's post “If you are asking why you...”
  (12 votes)
Aaryan Tiwari
Posted 4 months ago. Direct link to Aaryan Tiwari's post “Do you guys like to answe...”
Do you guys like to answer in terms of pi or do you guys like to get the answer in a decimal?
Button navigates to signup pageButton navigates to signup page
(8 votes)
Answer
- TheReal3A
  Posted 4 months ago. Direct link to TheReal3A's post “If you are using that val...”
  If you are using that value for another calculation, it's better to leave it in exact form (like you said, in terms of pi). Otherwise, probably show the answer as a decimal to a certain amount after putting it in the calculator.
  
  You don't want to round an answer that's used for further calculations as you lose some well-needed precision.
  Button navigates to signup page
  (9 votes)
nagappan.harshini123
Posted 2 years ago. Direct link to nagappan.harshini123's post “How to I find the diamete...”
How to I find the diameter of a circle when the circumference is given?
Button navigates to signup pageButton navigates to signup page
(7 votes)
Answer
- Janice Chan
  Posted 2 years ago. Direct link to Janice Chan's post “Just divide the circumfer...”
  Just divide the circumference by pi or 3.14.
  Comment on Janice Chan's post “Just divide the circumfer...”
  (3 votes)

MAP Recommended Practice

Course: MAP Recommended Practice > Unit 8

Radius, diameter, & circumference

What is a circle?

Radius of a circle

Diameter of a circle

Circumference of a circle

Using the formula $C = π d$ ‍

Challenge problem

Want to join the conversation?

MAP Recommended Practice

Course: MAP Recommended Practice > Unit 8

What is a circle?

Radius of a circle

Diameter of a circle

Circumference of a circle

Using the formula C=πd‍

Challenge problem

Want to join the conversation?

Using the formula $C = π d$ ‍