It all depends on how you view easy as. If you haven't learnt circumference for a while or are new to the subject, some people can find it challenging.

my district says this is 7th grade material

how to tell if your answer to circumference is correct

To find area with circumference, you divide the circumference by pi, to get your diameter. Then, you find the radius by dividing the diameter by 2. You then multiply your radius by itself and multiply that product by pi. Hope this Helps! :)

why do we need to measure circles

You don't really, but if you need to find your tire size, that's the way to do it. Also, a lot of math you won't really need for practicality, but you'll need it for high school which eventually leads up to college and your future job.

What should I do ,I need help

You should watch all of the videos again; they will help! If you are still having trouble, ask your teacher or your parent to help you!

Is the answer in the second practice question wrong? My calculator said 9π is 28.27, not 28.26. Ps: if it is wrong I don't see a way to report it.

If you use π then you will get 28.27. If you use 3.14 then you will get 28.26.

hey i need help i don't understand can someone help me this is on my finals

and for area mutiply the radius by itself then multiply it by pie (3.14)

yall why are the questions from 4 years ago-

The questions with the most votes are 4 years old, but if you go to the Sort by: and choose Recent, you will see questions that are 9, 10, and a month ago. Recent questions generally do not get many votes.

Who made pie because whoever did must of been really smart

No one really made it, Archimedes of Syracuse, was the first to calculate it.

Main content

Circumference review

Google Classroom

Review the basics of circumference and try some practice problems.

What is circumference?

Circumference is the distance around the outside of a circle (its perimeter!).

Want a review of circle vocabulary terms (like pi, radius, and diameter)? Check out this video.

Finding circumference of a circle

To find the circumference of a circle, we can use either of the following formulas:

start text, C, i, r, c, u, m, f, e, r, e, n, c, e, end text, equals, pi, times, start text, d, i, a, m, e, t, e, r, end text

start text, C, i, r, c, u, m, f, e, r, e, n, c, e, end text, equals, 2, times, pi, times, start text, r, a, d, i, u, s, end text

Want to know why these formulas work? Check out this article.

Example 1: Finding circumference when given diameter

Find the circumference of a circle with a diameter of start color #1fab54, 3, end color #1fab54.

The formula for the circumference of a circle that uses diameter is:

C, equals, pi, start color #1fab54, d, end color #1fab54
C, equals, pi, start color #1fab54, 3, end color #1fab54
C, equals, start color #11accd, 3, pi, end color #11accd

We can stop here and write our answer as start color #11accd, 3, pi, end color #11accd. Or we can plug in 3, point, 14 for pi and multiply.

C, equals, 3, point, 14, dot, 3
C, equals, start color #11accd, 9, point, 42, end color #11accd units

The circumference of the circle is start color #11accd, 3, pi, end color #11accd units or start color #11accd, 9, point, 42, end color #11accd units.

Example 2: Finding circumference when given radius

Find the circumference of a circle with a radius of start color #7854ab, 8, end color #7854ab.

The formula for the circumference of a circle that uses radius is:

C, equals, 2, pi, start color #7854ab, r, end color #7854ab
C, equals, 2, pi, start color #7854ab, 8, end color #7854ab
C, equals, start color #11accd, 16, pi, end color #11accd

We can stop here and write our answer as start color #11accd, 16, pi, end color #11accd. Or we can plug in 3, point, 14 for pi and multiply.

C, equals, 3, point, 14, dot, 16
C, equals, start color #11accd, 50, point, 24, end color #11accd units

The circumference of the circle is start color #11accd, 16, pi, end color #11accd units or start color #11accd, 50, point, 24, end color #11accd units.

Practice

Problem 1

Current

Suppose the radius of a circle is start color #7854ab, 5, end color #7854ab. What is its circumference?
Either enter an exact answer in terms of pi or use 3, point, 14 for pi and enter your answer as a decimal.

Want to try some more circumference of circle problems? Check out this exercise.

Want to join the conversation?

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Kamran Pallier
Posted 7 years ago. Direct link to Kamran Pallier's post “It all depends on how you...”
It all depends on how you view easy as. If you haven't learnt circumference for a while or are new to the subject, some people can find it challenging.
Button navigates to signup pageComment on Kamran Pallier's post “It all depends on how you...”
(207 votes)
Answer
- zonwujuba
  Posted 6 years ago. Direct link to zonwujuba's post “my district says this is ...”
  my district says this is 7th grade material
  Comment on zonwujuba's post “my district says this is ...”
  (6 votes)
libwhac30
Posted 6 years ago. Direct link to libwhac30's post “how to tell if your answe...”
how to tell if your answer to circumference is correct
Button navigates to signup pageComment on libwhac30's post “how to tell if your answe...”
(25 votes)
Answer
- Aris13
  Posted 5 years ago. Direct link to Aris13's post “To find area with circumf...”
  To find area with circumference, you divide the circumference by pi, to get your diameter. Then, you find the radius by dividing the diameter by 2. You then multiply your radius by itself and multiply that product by pi.
  Hope this Helps! :)
  Comment on Aris13's post “To find area with circumf...”
  (21 votes)
garciadavid
Posted 6 years ago. Direct link to garciadavid's post “why do we need to measure...”
why do we need to measure circles
Button navigates to signup pageComment on garciadavid's post “why do we need to measure...”
(18 votes)
Answer
- Blake S
  Posted 6 years ago. Direct link to Blake S's post “You don't really, but if ...”
  You don't really, but if you need to find your tire size, that's the way to do it. Also, a lot of math you won't really need for practicality, but you'll need it for high school which eventually leads up to college and your future job.
  Comment on Blake S's post “You don't really, but if ...”
  (33 votes)
Hanabi
Posted 5 years ago. Direct link to Hanabi's post “Is the answer in the seco...”
Is the answer in the second practice question wrong?
My calculator said 9π is 28.27, not 28.26.

Ps: if it is wrong I don't see a way to report it.
Button navigates to signup pageComment on Hanabi's post “Is the answer in the seco...”
(12 votes)
Answer
- 106s.ewells
  Posted 5 years ago. Direct link to 106s.ewells's post “If you use π then you wil...”
  If you use π then you will get 28.27.
  If you use 3.14 then you will get 28.26.
  Comment on 106s.ewells's post “If you use π then you wil...”
  (21 votes)
chloe.engle
Posted 7 years ago. Direct link to chloe.engle's post “What should I do ,I need ...”
What should I do ,I need help
Button navigates to signup pageComment on chloe.engle's post “What should I do ,I need ...”
(13 votes)
Answer
- 𝔸𝕟𝕘𝕖𝕝 ℤ𝕙𝕠𝕦
  Posted 2 years ago. Direct link to 𝔸𝕟𝕘𝕖𝕝 ℤ𝕙𝕠𝕦's post “You should watch all of t...”
  You should watch all of the videos again; they will help!
  
  If you are still having trouble, ask your teacher or your parent to help you!
  Comment on 𝔸𝕟𝕘𝕖𝕝 ℤ𝕙𝕠𝕦's post “You should watch all of t...”
  (5 votes)
Jalon
Posted 4 years ago. Direct link to Jalon's post “hey i need help i don't u...”
hey i need help i don't understand can someone help me this is on my finals
Button navigates to signup pageComment on Jalon's post “hey i need help i don't u...”
(9 votes)
Answer
- mkdhensa
  Posted 3 years ago. Direct link to mkdhensa's post “and for area mutiply the ...”
  and for area mutiply the radius by itself then multiply it by pie (3.14)
  Comment on mkdhensa's post “and for area mutiply the ...”
  (9 votes)
venus
Posted 2 years ago. Direct link to venus's post “yall why are the question...”
yall why are the questions from 4 years ago-
Button navigates to signup pageButton navigates to signup page
(8 votes)
Answer
- David Severin
  Posted 2 years ago. Direct link to David Severin's post “The questions with the mo...”
  The questions with the most votes are 4 years old, but if you go to the Sort by: and choose Recent, you will see questions that are 9, 10, and a month ago. Recent questions generally do not get many votes.
  Button navigates to signup page
  (11 votes)
Kenny Rhine
Posted 3 years ago. Direct link to Kenny Rhine's post “Who made pie because whoe...”
Who made pie because whoever did must of been really smart
Button navigates to signup pageComment on Kenny Rhine's post “Who made pie because whoe...”
(7 votes)
Answer
- KC
  Posted 3 years ago. Direct link to KC's post “No one really made it, Ar...”
  No one really made it, Archimedes of Syracuse, was the first to calculate it.
  Comment on KC's post “No one really made it, Ar...”
  (9 votes)
yasmine
Posted 5 months ago. Direct link to yasmine's post “can we ban math from scho...”
can we ban math from schools?
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(8 votes)
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- ImTerry
  Posted 5 months ago. Direct link to ImTerry's post “No, maybe get better at m...”
  No, maybe get better at math
  Comment on ImTerry's post “No, maybe get better at m...”
  (6 votes)
20.cordovaeduardo
Posted 4 years ago. Direct link to 20.cordovaeduardo's post “why era there so much kha...”
why era there so much khan academy assinments
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- ferminmundo
  Posted a year ago. Direct link to ferminmundo's post “im sorry it was my fault”
  im sorry it was my fault
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  (5 votes)

Geometry (all content)

Course: Geometry (all content) > Unit 7