  # Find the Circumference of a Circle

In this worksheet, students will calculate the circumference of a circle using pi and use this skill to solve simple problems. Key stage:  KS 4

GCSE Subjects:   Maths

GCSE Boards:   AQA, Eduqas, Pearson Edexcel, OCR,

Curriculum topic:   Geometry and Measures, Mensuration

Curriculum subtopic:   Mensuration and Calculation Perimeter Calculations

Difficulty level:   #### Worksheet Overview

Who invented the round table?

Sir Cumference! The circumference of a circle simply means the distance around the circle.  It can also be called the perimeter of the circle.

There are a few other things you need to know:

Diameter The diameter is the line that cuts through the centre of the circle. The radius comes from the centre of the circle to the edge and is half the diameter.

Pi No, not that pie, this one: You will need to learn the value for this..sorry. Did you know that pi is infinite - some people can quote it to hundreds of decimal places?

Lucky for you that you only need to use it to 3 decimal places, which is 3.142

Finally, you need the formula for finding the circumference of a circle:

Circumference of a circle  = pi x diameter  or C = pi x d

A great way to remember it is Cherry Pies are delicious! Building a toolbox is useful.  Builders have them, and so do mathematicians as we are building our knowledge.

Our toolbox contains definitions for circumference, perimeter, diameter, radius, pi and the formula.

Let's get started. Calculate the circumference of this circle.

Pi x diameter

3.142 x 14 = 43.988 cm  (43.99 cm to 2 decimal places)

You will be asked to round to decimal places or significant figures.

Warning! You might get a question that gives you the radius.

Remember that the radius is only half of the diameter, so double it first.

Calculate the circumference of a circle with a radius of 3 cm.

3 + 3 = 6 cm diameter

Now apply the formula: Pi x diameter

3.142 x 6 = 18.852  (18.9 to 3 significant figures)

You can use the pi button on your calculator for many calculations, but for this activity take the value of pi to be 3.142

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