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Perimeter and Area. Lesson 10-1. Area. Area is the amount of space inside a figure. We use square units to describe area. For rectangles, the area formula is A= lw (area equals length times width).

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Perimeter and area

Perimeter and Area

Lesson 10-1

Perimeter and area

  • Area is the amount of space inside a figure. We use square units to describe area.

  • For rectangles, the area formula is A=lw (area equals length times width).

  • For squares, the formula is still A=lw. However, since every side of a square is the same, then it can also be expressed as A=s2 where s equals the length of one side.


12 m



8 m

A=96 sq. m

Area is expressed in square units. It can be written (in this case) as 96 sq. m or 96 m2.

Area of irregular shapes
Area of Irregular Shapes

Count how many squares are completely covered by the shape. Put partial squares together to make wholes.

  • 13 squares are full.

  • 2 squares are almost full, and they can be matched up with 2 squares that are almost empty.

  • 3 squares are about half full – when two are put together that makes a full square. The half square is left over.

  • Altogether, there are 16 and a half squares full.


  • Perimeter is the distance around the outside of a figure.

  • The perimeter of a rectangle is derived by adding all four sides. Since the two lengths are equal, and the two widths are equal, then it can be written as P = 2l + 2w.

  • For squares, the perimeter is found the same way (add all 4 sides). Since all sides are the same, however, you can use the formula P = 4s.

  • Any irregular figures, just add up all the sides.


18 cm

5 cm

5 cm

P = 2w + 2l

18 cm

P = 2(5) + 2(18)

Perimeter results in regular units, not square units.

P = 10 + 36

P = 46 cm