Perimeter

Test yourself

Perimeter

The perimeter of a shape is the 'outside' of the shape. You need to add all of the lengths of the shape.

Example 1

To find the perimeter of this shape, we need to add all the side lengths together.

Example 1 cont.

Example 2

To find the perimeter of this shape, we need to add all the side lengths.

Example 2 cont.

Missing length

Sometimes you might need to work out the missing length of a shape in order to find the perimeter.
What is the perimeter of the rectangle above?

Missing length

We use the information that rectangles have two pairs of sides of equal length to work out that the length of the missing side is 4 cm.

Perimeter of Composite Shapes

A composite shape can be made when two or more shapes are put together.

Example

This is a composite shape made up of two rectangles.

Perimeter of composite shapes

To find the perimeter. you must first work out the length of the missing sides.

Length of side a

To work out the length of side a, you need to look at how long the length of the shape is altogether.
- You can see that the longest verticle side is 6 m.
- You need to match with the other verticle side, which is 3 m long.
  - 3 m + ? = 6 m
  - So, side a is 3m long.

Length of side b

To work out the length of side b, you need to look at how long the two horizontal lengths are.
- The horizontal lengths are 4 m and 5 m.
  - 4 m + 5 m = 9 m
  - So, side b is 9 m long.

Calculating the perimeter

You can now calculate the perimeter by adding all the lengths on the 'outside' of the shape.

1Year 3 - Number

2Year 3 - Measurement

2.1Length

2.1.1Length

2.1.2Comparing Lengths

2.1.3Add & Subtract Lengths

2.1.4Perimeter

2.2Mass

2.2.1Mass

2.2.2Comparing Masses

2.2.3Add & Subtract Masses

2.3Volume & Capacity

2.3.1Volume & Capacity

2.3.2Comparing Volumes

2.3.3Add & Subtract Volumes

2.4Money

2.4.1Money

2.4.2Counting Money

2.4.3Adding & Subtracting Money

2.5Time

2.5.1Units of Time

2.5.2Clocks

2.5.3Telling the Time

2.5.4Time of the Day

2.5.512-Hour & 24-Hour Clocks

2.5.6Measuring Time

3Year 3 - Geometry

3.1Angles

3.1.1Angles in Degrees

3.1.2Types of Angle

3.2Properties of Shapes

3.2.12D Shapes

3.2.23D Shapes

3.3Straight Lines

3.3.1Straight Lines

3.3.2Parallel & Perpendicular Lines

4Year 3 - Statistics

4.1Statistics

4.1.1Statistics

4.1.2Pictograms & Bar Charts

5Year 4 - Number

6Year 4 - Measurement

6.1Units

6.1.1Metric Measurements

6.1.2Adding & Subtracting Money

6.2Time

6.2.1Converting Units of Time

6.2.2Changing the 12-Hour Clock to the 24-Hour Clock

6.2.3Changing the 24-hour Clock to the 12-Hour Clock

7Year 4 - Geometry

7.1Properties of Shapes

7.1.1Symmetry

7.1.2Types of Triangle

7.1.3Quadrilaterals

7.2Perimeter & Area

7.2.1Perimeter

7.2.2Area

7.3Position & Direction

7.3.1Coordinates

7.3.2Translation

8Year 4 - Statistics

8.1Statistics

8.1.1Types of Data

8.1.2Pictograms & Bar Charts

8.1.3Line Graphs

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