I need help..... if the circumference is a low number like 2, doesn't that make the diameter and radius a decimal which also makes the area a decimal? If not, how do you do it? I just don't understand it.

Well, actually it's quite simple! When diameter is 2 cm Then, Radius = 1cm Therefore, A=(pi)r^2 =(pi)*r*r =3.14*1*1 =3.14 (approx.) But, if Radius < 1cm, Then the value of r*r is also a decimal. If, Diameter is 0.5cm The r=2.5cm Therefore, the Area is (pi)r^2 A = (pi)0.25*0.25 = 0.0625(pi) There is no rule that if Radius or Diameter is a decimal, then the Area and the Circumference is also decimal but it ALMOST always shows up that way. Even if it is a decimal no difference. You just have to be careful with all those decimal points!

Area is much simpler than i expected. Once you've remembered the formula it becomes very easy!

agreed. once you remember (pi)*radius^2 it's soo easy especially if you don't try to use 3.14 and just put, for instance, 3(pi)

im so done my teacher bad

the diameter is the radius but time 2, the radius is half of the diameter, and the circumference is the radius squared times by pi

How could I get the exact circumference? Is it possible

That is a very interesting question. I don't think you can because the circumference of a number is pi times the diameter. Pi is never ending and computers can "only" find like 50 billion digits. I don't think any number multiplies into an infinitely long number perfectly.

My teacher would not teach us this yet I have NO idea what this means or what to do

If you dont get it the formula for area is r*r*3.14= a and the circumference is d*3.14= c r= radius d= diameter c= circumference a= area

Is the area of a circle is pi×r squared or 2 pi r. I am confused. Thanks to those who respond.

Remember that circumference (which is a distance) has length units, and area has square length units. Because the radius r has length units, the previous sentence should help you remember that circumference is 2 pi r, and area is pi r^2. Have a blessed, wonderful day!

Either enter an exact answer in terms of \piπpi or use 3.143.143, point, 14 for \piπpi and enter your answer as a decimal.

That is a wrong Pi approximation, brob1. Actual Pi = 3.14159265... The numbers after the decimal never repeat in a pattern because Pi is an irrational number.

Main content

Area of circles review

Q: Area is much simpler than i expected. Once you've remembered the formula it becomes very easy!

agreed. once you remember (pi)*radius^2 it's soo easy especially if you don't try to use 3.14 and just put, for instance, 3(pi)

Q: im so done my teacher bad

the diameter is the radius but time 2, the radius is half of the diameter, and the circumference is the radius squared times by pi

Q: How could I get the exact circumference? Is it possible

That is a very interesting question. I don't think you can because the circumference of a number is pi times the diameter. Pi is never ending and computers can "only" find like 50 billion digits. I don't think any number multiplies into an infinitely long number perfectly.

Q: My teacher would not teach us this yet I have NO idea what this means or what to do

If you dont get it the formula for area is r*r*3.14= a and the circumference is d*3.14= c r= radius d= diameter c= circumference a= area

Q: Is the area of a circle is pi×r squared or 2 pi r. I am confused. Thanks to those who respond.

Remember that circumference (which is a distance) has length units, and area has square length units. Because the radius r has length units, the previous sentence should help you remember that circumference is 2 pi r, and area is pi r^2. Have a blessed, wonderful day!

Q: Either enter an exact answer in terms of \piπpi or use 3.143.143, point, 14 for \piπpi and enter your answer as a decimal.

That is a wrong Pi approximation, brob1. Actual Pi = 3.14159265... The numbers after the decimal never repeat in a pattern because Pi is an irrational number.

Google Classroom

Review the basics of area of circles and try some practice problems.

Area of a circle

The area of a circle is the amount of space the circle covers. We can also think of it as the total amount of space inside the circle.

To find the area of a circle, we can use the following formula:

start text, A, r, e, a, space, o, f, space, c, i, r, c, l, e, end text, equals, pi, times, start text, r, a, d, i, u, s, end text, squared

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

Want to learn more about finding area of circles? Check out this video.

Example 1: Finding area when given radius

Find the area of a circle with a radius of start color #11accd, 5, end color #11accd.

The equation for the area of a circle is:

A, equals, pi, r, squared
A, equals, pi, dot, start color #11accd, 5, end color #11accd, squared
A, equals, pi, dot, 25

We can stop here and write our answer as 25, pi. Or we can plug in 3, point, 14 for pi and multiply.

A, equals, 3, point, 14, dot, 25
A, equals, 78, point, 5 square units

The area of the circle is 25, pi square units or 78, point, 5 square units.

Example 2: Finding area when given diameter

Find the area of a circle with a diameter of start color #1fab54, 16, end color #1fab54.

First, let's find the radius:

\begin{aligned} r &= \dfrac d2 \\ \\ r &= \dfrac{\greenD{16}}{2} \\ \\ r &= \blueD{8} \end{aligned}

Now we can find the area.

The equation for the area of a circle is:

A, equals, pi, r, squared
A, equals, pi, dot, start color #11accd, 8, end color #11accd, squared
A, equals, pi, dot, 64

We can stop here and write our answer as 64, pi. Or we can plug in 3, point, 14 for pi and multiply.

A, equals, 3, point, 14, dot, 64
A, equals, 200, point, 96 square units

The area of the circle is 64, pi square units or 200, point, 96 square units.

Practice

Problem 1

Current

Find the area of a circle with a radius of start color #11accd, 7, end color #11accd.
Either enter an exact answer in terms of pi or use 3, point, 14 for pi and enter your answer as a decimal.

unitssquared

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

Want to join the conversation?

Sort by:

Maxwell(Max)
Posted 6 years ago. Direct link to Maxwell(Max)'s post “I need help..... if the c...”
I need help..... if the circumference is a low number like 2, doesn't that make the diameter and radius a decimal which also makes the area a decimal? If not, how do you do it? I just don't understand it.
Button navigates to signup pageComment on Maxwell(Max)'s post “I need help..... if the c...”
(31 votes)
Answer
- sasipgis
  Posted 3 years ago. Direct link to sasipgis's post “Well, actually it's quite...”
  Well, actually it's quite simple!
  
  When diameter is 2 cm
  Then, Radius = 1cm
  Therefore, A=(pi)r^2
  =(pi)*r*r
  =3.14*1*1
  =3.14 (approx.)
  
  But, if Radius < 1cm,
  Then the value of r*r is also a decimal.
  
  If, Diameter is 0.5cm
  The r=2.5cm
  Therefore, the Area is (pi)r^2
  A = (pi)0.25*0.25
  = 0.0625(pi)
  
  There is no rule that if Radius or Diameter is a decimal, then the Area and the Circumference is also decimal but it ALMOST always shows up that way.
  
  Even if it is a decimal no difference.
  You just have to be careful with all those decimal points!
  Comment on sasipgis's post “Well, actually it's quite...”
  (28 votes)
espinor004
Posted 2 years ago. Direct link to espinor004's post “i like math **sobs in th...”
i like math

*sobs in the corner while trying to find the answer*
Button navigates to signup pageComment on espinor004's post “i like math **sobs in th...”
(17 votes)
Answer
- Arjun patil
  Posted 9 months ago. Direct link to Arjun patil's post “no cap”
  no cap
  Button navigates to signup page
  (4 votes)
Yuyang Liang
Posted 5 years ago. Direct link to Yuyang Liang's post “How could I get the exact...”
How could I get the exact circumference? Is it possible
Button navigates to signup pageComment on Yuyang Liang's post “How could I get the exact...”
(5 votes)
Answer
- Charlie Hu
  Posted 5 years ago. Direct link to Charlie Hu's post “That is a very interestin...”
  That is a very interesting question. I don't think you can because the circumference of a number is pi times the diameter. Pi is never ending and computers can "only" find like 50 billion digits. I don't think any number multiplies into an infinitely long number perfectly.
  Comment on Charlie Hu's post “That is a very interestin...”
  (21 votes)
abigail.2458521
Posted 3 years ago. Direct link to abigail.2458521's post “Area is much simpler than...”
Area is much simpler than i expected. Once you've remembered the formula it becomes very easy!
Button navigates to signup pageComment on abigail.2458521's post “Area is much simpler than...”
(10 votes)
Answer
- Ellie
  Posted 7 months ago. Direct link to Ellie's post “agreed. once you remember...”
  agreed. once you remember (pi)*radius^2 it's soo easy
  especially if you don't try to use 3.14 and just put, for instance, 3(pi)
  Comment on Ellie's post “agreed. once you remember...”
  (2 votes)
Rosy
Posted 3 months ago. Direct link to Rosy's post “'Would you rather uses Pi...”
'Would you rather uses Pi as a term or to use 3.14? I would rather use it as a term because it's much more simple.'
Button navigates to signup pageComment on Rosy's post “'Would you rather uses Pi...”
(7 votes)
Answer
- FilipK
  Posted 3 months ago. Direct link to FilipK's post “I like to use 3.14”
  I like to use 3.14
  Comment on FilipK's post “I like to use 3.14”
  (3 votes)
Iris C
Posted 2 years ago. Direct link to Iris C's post “im so done my teacher bad”
im so done my teacher bad
Button navigates to signup pageComment on Iris C's post “im so done my teacher bad”
(6 votes)
Answer
- 🥇😀🥇Connor Maines🥇😀🥇
  Posted 2 years ago. Direct link to 🥇😀🥇Connor Maines🥇😀🥇's post “the diameter is the radiu...”
  the diameter is the radius but time 2, the radius is half of the diameter, and the circumference is the radius squared times by pi
  Button navigates to signup page
  (3 votes)
cactus
Posted 6 months ago. Direct link to cactus's post “Baller”
Baller
Button navigates to signup pageComment on cactus's post “Baller”
(7 votes)
Answer
paytongroenewold
Posted 6 years ago. Direct link to paytongroenewold's post “My teacher would not teac...”
My teacher would not teach us this yet I have NO idea what this means or what to do
Button navigates to signup pageComment on paytongroenewold's post “My teacher would not teac...”
(3 votes)
Answer
- Yuyang Liang
  Posted 5 years ago. Direct link to Yuyang Liang's post “If you dont get it the fo...”
  If you dont get it the formula for area is r*r*3.14= a and the circumference is d*3.14= c
  r= radius d= diameter c= circumference a= area
  Comment on Yuyang Liang's post “If you dont get it the fo...”
  (7 votes)
brob1
Posted 4 years ago. Direct link to brob1's post “Either enter an exact ans...”
Either enter an exact answer in terms of \piπpi or use 3.143.143, point, 14 for \piπpi and enter your answer as a decimal.
Button navigates to signup pageComment on brob1's post “Either enter an exact ans...”
(1 vote)
Answer
- Denis Orlov
  Posted 4 years ago. Direct link to Denis Orlov's post “That is a wrong Pi approx...”
  That is a wrong Pi approximation, brob1.
  
  Actual Pi = 3.14159265... The numbers after the decimal never repeat in a pattern because Pi is an irrational number.
  Comment on Denis Orlov's post “That is a wrong Pi approx...”
  (6 votes)
SrPani
Posted 6 months ago. Direct link to SrPani's post “Is the area of a circle i...”
Is the area of a circle is pi×r squared or 2 pi r. I am confused. Thanks to those who respond.
Button navigates to signup pageComment on SrPani's post “Is the area of a circle i...”
(2 votes)
Answer
- Ian Pulizzotto
  Posted 6 months ago. Direct link to Ian Pulizzotto's post “Remember that circumferen...”
  Remember that circumference (which is a distance) has length units, and area has square length units. Because the radius r has length units, the previous sentence should help you remember that circumference is 2 pi r, and area is pi r^2.
  
  Have a blessed, wonderful day!
  Comment on Ian Pulizzotto's post “Remember that circumferen...”
  (9 votes)

MAP Recommended Practice

Course: MAP Recommended Practice > Unit 8