Components & Circumference of Circles
In order to find the
 diameter, multiply the
 radius by 2
d = 2r
In order to find the
radius, divide the
diameter by 2.
r = d÷2
cm
cm
cm
cm
ft
ft
in
in
m
m
m
m
To find circumference
multiply the diameter
by pi (3.14).
C = πd
Use 3.14 for pi (π)
cm
If you are given the
radius then multiply by 2
to find the diameter then
multiply by pi (3.14)
C = π(2r)
Use 3.14 for pi (π)
cm
Mixed Practice:
Remember:

C = πd
    or
C = π(2r)
Use 3.14 for pi (π)
m
Use 3.14 for pi (π)
in
Use 3.14 for pi (π)
in
Use 3.14 of pi (π)
in
In order to find the 
diameter of a circle, take
the circumference and
divide by pi (3.14)
Diameter = 
Use 3 for pi (π)
102 in
in
Diameter = 
Use 3.1 for pi (π)
136.4 m
m
In order to find the
radius, take the
circumference and divide
by pi (3.14). Then divide
by 2.
Radius = 
Diameter = 
Use 3 for pi (π)
138 cm
cm
cm
Diameter =
Radius = 
Use 3 for pi (π)
180 m
m
m
Since circumference is
found by diameter x π
then the number
attached to π is the
diameter. For example:
if C=12π then 12 is the
diameter.
A circle's circumference is 12π. What is the diameter?
The circumference of a circle 22π. What is the diameter?
Don't forget: to find the
radius you take the
diameter and divide by
2
The circumference of a circle is 18π. What is the radius?
The circumference of a circle is 32π. What is the radius?
The circumference of a circle is 13π. What is the 
diameter and the radius?
Diameter =
Radius =
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