Circumference of a Circle

About: A mechanical engineering graduate from JBU, I enjoy putting motors on things that don't already have them, tinkering with small gas engines, airsoft, paintball, and pyrotechnics. I am no longer active on thi...

In this instructable, you will learn how to find the circumference of a circle. It is a very simple process, but requires a scientific calculator or better, if you want to find the exact answer. You can also use your regular cheap calculator from walmart but you will be off on your answer a little bit. please pardon the spelling error, it should be circle, not cirle.

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Step 1: Find a Circle With the Dimensions

The first step is to find a circle. It helps if the circle has already written dimensions, but you only need the diameter, so it won't be that hard to find. This circle has dimentions already written on it.

Step 2: Find the Diameter

If you have a circle with the dimensions already written out, you may ignore this step. (Note: if you have a circle with pre written dimensions, they may not be to scale. I know it is like this in most math books. So do not worry if you have a circle that is tiny and says that it's diameter is 10 feet.) Now, if the circle does not have written dimensions, you will need a ruler to find the diameter. The diameter is the distance across the circle. Next, lay the ruler across the circle, and then take the measurement in your unit of choice. ( i would recomend centimeters for a small circle, it is more accurate). Now that you have the diameter, you may move on to the next step.

Please note: I just drew this circle, it is not perfect.

Step 3: Learn the Formula

In this step you will need to learn the formula for finding the circumfrence of a circle. The formula is:
Pi times (X) Diameter(what you found in the previous step). If you don't know what Pi is, don't worry, I will get to that later. I have found that the best way to remember this formula is to say "i have to go potty", because potty sounds a lot like "pi d," or Pi times diameter.

Step 4: Plugging in the Values

Now its time to plug the values into your calculator. This is when it helps to have a scientific calculator. If you have a scientific calculator, begin by pressing the Pi button. I would show you what it looks like, but there isn't a button on the keyboard for it, so the best I can do is put a picture of it. If you do not have a Pi button, dont worry, just plug in 3.14 in place of it, and your answer will be close. now hit the times (X) button on your calculator and plug in the diameter. Now hit equals (=), and POOF!!! theres your answer!

Step 5: Time for Some Examples

Now it is time for some examples! your diameter is 10 feet, so now its time to plug in the formula.formula:����������������� Pi X DiameterPlugged in formula����������������� Pi X 10������� or:����������������� 3.14 X 10now plug it in in your calculator. if you used Pi, you should get the answer 31.4159...... If you used 3.14, you should get 31.4 as your answer.

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    4 Discussions


    If you manually in a way or another try to measure the circumference of any circle and devide it by the diameter you will get pi, the more precise your measurement the more accurate pi will be, that's why you multiply diameter by pi to get the circumference.


    Reply 9 years ago on Introduction

    because pi is the rule for calculating circumference they figured out a pattern that worked for every circle.

    i don't know why they do it, or how it works, my math teacher said that is how it is so that is how it is and it gets the correct answer