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Perimeter is the word used to describe the distance around the outside of an object or shape.

You can use counting units to find the perimeter of a shape, by counting the number of sides that touch the outside of the shape.

 

Example

Find the perimeter of this square using
 counting units.

 

Count the number of sides that touch the outside of the square. There are 3 counting units on each side of the square and there are 4 sides to the square (3 + 3 + 3 + 3 = 12).

The perimeter is 12 units.

 

Area is the number of square units needed to cover a flat surface.

You can use counting units to find the area of a shape, by counting the number of squares inside of it.


1 square unit

 

Example

Find the area of this shape using
 counting units.
Count the number of squares in the whole shape.

The area is 13 square units because there are 13 squares in the shape.

Sometimes you need to count half squares to find the area of a figure.

Example

Find the area of this shape using
 counting units.

Count the number of whole squares in the shape first. Then count the half square.

The area is 8 1/2  square units .

 

Volume is the number of cubic units needed to fill a space figure.

You can use counting units to find the volume of a shape, by counting the number of cubes.


1 cubic unit

 

Example

Find the volume of this shape using
 counting units.

Count the number of cubes in the shape.

The volume is 5 cubic units.

 

Remember: You can use counting units to measure the perimeter, area, or volume of a shape or object.

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