Perimeter
Perimeter
The distance around the outside of a
shape is called the perimeter.
The units for perimeter are
mm, cm, m or km.
Find the perimeter of this shape if each square
is equal to one metre.
Click mouse to help count sides!
Perimeter = 24 metres
Try this one!
Count the
number of
sides to
determine the
perimeter of
this flat
object.
The
perimeter is
equal to 12.
Find the Perimeter
(Click the mouse when the man gets to the end of each side)
6 + 10
=16cm
6cm
10 cm
The perimeter
is…
6cm
22 + 10
= 32cm
32cm !
16 + 6
= 22cm
How do you find the perimeter of this rectangle?
8 cm
6 cm
First we need to find the
length of each side by
counting the squares.
6 cm
8 cm
The perimeter of the shape is 8 + 6 + 8 + 6 = 28cm.
Basic IWB resource using ruler to measure lengths
http://www.mathplayground.com/area_perimeter.html
(Select Play then Skip then Next to get straight onto activity)
http://www.shodor.org/interactivate/activities/PerimeterExplorer/
(Shape generator to find perimeter)
Find the Perimeter
 Add
up all sides of the object
5cm
2cm
P=2+2+5+5
P = 14cm
Find the Perimeter
3 mm
2 mm
P = 10 mm
Find the Perimeter
3cm
3cm
3cm
3cm
P = 12cm
Find the Perimeter
8m
8m
P = 32m
Find the Perimeter
(Click the mouse once to get the man all the way round the triangle)
8
The perimeter
is…
26
8cm
8cm
26 cm !
16
10 cm
Bonus question: Name this Triangle……. Isosceles
Find the Perimeter
3 cm
6 cm
5cm
P = 14 cm
Bonus question: Name
this Triangle…….
Right angled triangle
Find the Perimeter
4m
Bonus question:
Name this
Triangle…….
Equilateral triangle
4m
4m
P = 12 m
Find the Perimeter
(One click of the mouse will get the man all the way around the perimeter)
12
This is a regular
octagon with sides
4 cm
16
The perimeter
is…
20
8
4
32
32 cm !
24
28
Find the Perimeter
(One click of the mouse will get the man all the way around the perimeter)
This shape
has sides of
5 cm each
The perimeter
is…
60 cm !
12
sides
Now find the
perimeter of these
shapes. They are
not drawn to
scale.
5cm
3cm
3cm
4cm
3cm
7cm
3cm
7cm
3cm
3cm
Perimeter = 18cm
4cm
3cm
3cm
3cm
3cm
4cm
4cm
3cm
Perimeter = 22cm
Perimeter = 28cm
Now look at those two pools. Family A has 8 squares to
swim in and Family B only has 7 squares to swim but
which family has more side panels of the pool to clean?
The perimeter of Family A’s pool is 12 units long.
The perimeter of Family B’s pool is 14 units long.
Therefore, Family B has more side
panels of the pool to clean.
Family A
Family B
8
7
Your Turn

http://www.funbrain.com/cgibin/poly.cgi?A1=s&A2=0&A15=1&INSTRUCTS=1
(Easy perimeter game using ruler)

http://www.khanacademy.org/math/geometry/ba
sic-geometry/e/perimeter_1
(Khan academy: very easy perimeter questions)
http://www.youtube.com/watch?v=KwXBMGdSWmI
(Perimeter Song)
Finding Missing Vertical Lengths
4
?
Step 1: label vertical sides
Step 2: Slide these sides to find
missing side.
15
20
12
?
? = 20 – 12
=8
Finding Missing Horizontal Lengths
4
?
Step 1: label horizontal sides
Step 2: Slide these sides to find
missing side.
15
20
12
?
? = 4 + 15
= 19
Video explanation of how to find
perimeter of compound shapes
http://www.youtube.com/watch?v=vqDpxw
WehuE
Extension: Find the perimeter
11 – 5 = 6cm
1) We need to find the distance
around the outside of the shape
but two lengths are missing.
3cm
2) Find the missing lengths.
3) Add all the lengths as usual.
11cm
4cm
5cm
Perimeter = 3 + 6 + 4 + 5 + 7 + 11
= 36cm
3 + 4 = 7cm
Thanks
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