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What Is the Perimeter?(With Examples)

Perimeter is the total distance around the outside of a two-dimensional shape. It is found by adding up the lengths of all the sides. For circles, the perimeter is called the circumference. Perimeter is measured in linear units (cm, m, in, ft, etc.).

Grades 3-6Key Stage 2 (Year 3-6)Årskurs 3-6Klasse 3-6

📖Definition

📐Formula

Rectangle: P = 2(l + w); Square: P = 4s; Circle: C = 2πr

For rectangles, add length and width then multiply by 2. For squares, multiply one side by 4. For circles, the circumference equals 2 times pi times the radius.

📝Step-by-Step Guide

Identify All Sides

Count how many sides the shape has and find the length of each side.

Add All Side Lengths

For polygons, add up all the side lengths. Make sure all measurements use the same unit.

Use Formulas for Regular Shapes

For rectangles: P = 2l + 2w or P = 2(l + w). For squares: P = 4s.

For Circles Use Circumference

Circumference = 2πr or πd, where r is radius and d is diameter.

C = 2πr = πd

⚠️Common Mistakes to Avoid

Confusing perimeter with area
Forgetting to include all sides
Using square units instead of linear units
For circles, confusing radius with diameter
Not converting all measurements to the same unit first

✏️Practice Problems

Easy

Find the perimeter of a rectangle with length 7 cm and width 4 cm

Answer: 22 cm

Medium

Find the circumference of a circle with radius 5 m (use π = 3.14)

Answer: 31.4 m

Hard

A rectangle has perimeter 36 cm. If the length is twice the width, find the dimensions.

Answer: Length = 12 cm, Width = 6 cm

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Area Circles Polygons Measurement

Curriculum Alignment

CommonCore (3.MD.D.8)KS3KMK

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