The perimeter of a shape is the distance around it. You can imagine that there is a fence built around the shape and you want to find out how long the fence should be. That is what the perimeter is! Once you know the formula for finding the perimeter of a shape, you can apply it and find the perimeter with any numbers.
SQUARE
A square has 4 sides that are the same length. Since the perimeter is the length of the fence around the shape, you will need 4 pieces that are the length of one side.
length + length + width + width = 2 x length + 2 x width
RECTANGLE
A rectangle is like a square because it is basically a stretched out square. This means that 2 sides will be longer than the other 2. We can call the longer sides the length and the shorter sides the width. To make a fence around a rectangle, we would therefore need 2 pieces equal to the length and 2 pieces equal to the width.
side 1 + side 2 + side 3
TRIANGLE
A triangle has 3 sides and sometimes all sides have the same length, or only 2 sides have the same length, or all sides have different lengths.
You can just add the 3 sides together in all cases.
side 1 + side 2 + side 3
IRREGULAR SHAPE
If the shape is not something common like a square, triangle, or rectangle, you can just add all the different lengths together.
side 1 + side 2 + side 3 + side 4 + side 5 + side 6 + side 7
TOP TIP
You can always add all the sides of the shape together as a shortcut if you forget the formula. However, the formulas will help you with your problem solving in later stages of math, so it’s always useful to know them.
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