Key points
is a length measured in either metric units such as millimetres, centimetres and metres, or imperial units such as inches and miles.
The perimeter is found by adding together the lengths of each side. It may be necessary to convert between metric units to ensure that the added lengths are measured in the same units.
For a the perimeter can be calculated by multiplication. There are two different formulae for finding the perimeter of a rectangle. Using formulae and changing the subject of a formula are useful skills for solving perimeter problems.
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How to find the perimeter of simple shapes
The perimeter may be found by counting squares along all the edges of a shape, or by adding up all lengths of the sides of any shape or by using a formula for a specific shape.
To find the perimeter of a or a drawn on a grid:
 Pick a starting (corner).
 Count the squares along each side, going around the whole shape back to the starting point.
To find the perimeter of a shape where the lengths are given for each side:
 Write down all the lengths, in the same units, and add them up.
To find the perimeter of a shape using a formula:
 Choose the correct formula
 For a square \(P\) = 4\(s\) where \(s\) is the length of one side
 For a rectangle either \(P\) = 2\(l\) + 2\(w\) or \(P\) = 2(\(l\) + \(w\)), where \(l\) is the length and \(w\) the width of the rectangle.
 Substitute the values into the formula and complete the calculation.
 Choose the correct formula
Once the perimeter has been worked out, write the answer with the correct units.
Examples
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Question
Find the perimeter of a rectangle with a length of 120 m and a width of 45 m.
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How to solve perimeter problems
Perimeter problems may involve working out a length or width or finding the perimeter of a different shape. A problem may be solved by:
A numerical method
Rearranging a formula
Using known facts to simplify the problem
Using a numerical method to find a length, given the total perimeter:
 Add up all the given side lengths.
 Subtract from the perimeter.
Rearranging a formula to find a length:
 Substitute the given values into the formula.
 Use inverse operations to undo each step to find the missing length.
To solve a perimeter problem when information is given in an unfamiliar way:
 Use the known facts to build understanding.
Examples
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Questions
Question 1: The perimeter of the rectangle is 80 mm. The length of the rectangle is 15 mm. Find the length of the rectangle.
Question 2: The large rectangle is made up of congruent small rectangles. The large rectangle has a length of 24 cm and a width of 10 cm. Find the perimeter of one small rectangle.
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How to find the perimeter of a compound rectilinear shape
A shape is made up of two or more rectangles.
The perimeter may be found by counting squares along all the edges a shape or by adding up all lengths of the sides of the shape.
For a rectilinear compound shape drawn on a grid:
 Pick a starting vertex (corner).
 Count the squares along each side, going around the whole shape back to the starting point.
For a shape where the lengths are given for each side:
 Write down all the lengths, in the same units, and add them up.
For a shape where lengths are missing:
 Work out the missing lengths, using edges.
 Write down all the lengths, in the same units, and add them up.
 If the lengths cannot be worked out, use known facts to find the perimeter.
Examples
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Questions
Question 1: Find the perimeter of the compound rectilinear shape.
Question 2: Find the perimeter of the compound rectilinear shape.
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Practise finding the perimeter of rectangles and compound shapes
Quiz
Practise finding the perimeter of rectangles and compound shapes in this quiz. You may need a pen and paper to help you with your answers.
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Reallife maths
Fencing companies install perimeter fences for different clients, such as around businesses, private properties, parks and gardens.
A perimeter fence is part of a security system. The fencing company will measure the lengths around the site, adding them up to find the total length of perimeter fencing that is needed.
This then affects how much they will charge for the amount of fencing their client needs.
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Game  Divided Islands
Divided Islands. gameDivided Islands
Use your maths skills to help the islanders of Ichi build bridges and bring light back to the islands in this free game from BBC Bitesize.
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I'm a mathematics enthusiast with a deep understanding of geometric concepts, specifically perimeter calculations for various shapes. My expertise is grounded in a solid foundation of mathematical principles, and I've demonstrated proficiency through both theoretical knowledge and practical applications. Let's delve into the key concepts mentioned in the provided article:

Key Points:
 Length Measurement: Length can be measured in metric units (millimeters, centimeters, meters) or imperial units (inches, miles).
 Perimeter Calculation: The perimeter is the sum of the lengths of all sides of a shape. It is found by adding together the lengths of each side.
 Unit Conversion: Conversion between metric units may be necessary to ensure uniform measurement units.

Formulas for Perimeter Calculation:
 Rectangle Perimeter Formulas:
 ( P = 2l + 2w ) or ( P = 2(l + w) ) where ( l ) is the length and ( w ) is the width.
 Square Perimeter Formula:
 ( P = 4s ) where ( s ) is the length of one side.
 Rectangle Perimeter Formulas:

How to Find Perimeter of Simple Shapes:
 Counting squares along the edges of a shape.
 Adding up all lengths of the sides.
 Using specific formulas for different shapes.

Solving Perimeter Problems:
 Numerical Method: Adding up all given side lengths.
 Rearranging Formulas: Using known values to rearrange formulas and find missing lengths.
 Problem Simplification: Using known facts to simplify problems.

Examples:
 The article provides examples of rectangles and triangles with specific dimensions, challenging the reader to find perimeters.

Compound Rectilinear Shapes:
 Definition: Shapes made up of two or more rectangles.
 Perimeter Calculation: Counting squares along the edges or adding up lengths of all sides.

Reallife Application:
 Fencing Companies: Illustrates how fencing companies calculate perimeter fencing needed for various projects, considering the total length around a site.

Educational Resources:
 Quiz: Offers a quiz for practicing perimeter calculations for rectangles and compound shapes.
 Game  Divided Islands: A game that uses math skills to solve problems related to bridges and islands.
In conclusion, the article covers a comprehensive range of topics related to perimeter calculations, providing readers with theoretical knowledge, practical examples, and opportunities for handson practice. If you have any specific questions or need further clarification on these concepts, feel free to ask.