Introduction: Circumference of a Circle
In this Instructable, we will dive into the exciting world of Circles.
Specifically the Circumference of a Circle.
Supplies:
Pencil (needed for it's erase-ability)
Paper
Calculator (to check your answer)
Step 1: Circle
Some basics of the Circle:
Circumference - the distance around the circle (aka the perimeter of the circle)
Radius - the distance from the center to any point on the circle
Diameter - the distance from a point on the circle to another point on the circle going
through the center (also twice the length of the Radius)
Pi - the symbol that represents the value 3.14 (actually Pi is a never ending number, but for our purposes 3.14 will be fine)
Step 2: Circumference
Now to find the Circumference
Formulas for Circumference:
C = 2*Pi*r
C = Pi*d
r - radius
d - diameter
General Steps for solving:
1) write the formula you will use
2) write the information Given
3) substitute the given information into the formula
4) follow your Order of Operations (PEMDAS) to simplify and reduce
5) circle your answer
6) check your answer
Example 1:
Given: circle with a radius = 4 cm
1) C = 2*Pi*r (choose this formula because you are given a radius)
2) r = 4
3) C = 2*Pi*4
4) C = 8*Pi
4) C = 8*3.14
5) C = 25.12 cm (don't forget your units)
Example 2:
Given: circle with a diameter = 12 in.
1) C = Pi*d (choose this formula because you are given a diameter)
2) d = 12
3) C = Pi*12
4) C = 3.14*12
5) C = 37.68 in. (don't forget your units)

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7 Comments
10 years ago
3.1415926535897932384626433832795028841961693993751058209749445923078164062862089986280348
10 years ago
Ive got 88! Memorized it fir a contest.
3.1415926535897932384626433732795028841971693993751058209749445923078164062862089986280348
Plz tell me if i messed up
14 years ago on Introduction
off the top of my head, pi is equal to 3.141592653589793. i have it to a million on my comp
Reply 13 years ago on Introduction
I only have it memorized to 3.14159. I like to show my students the websites that let you search for your b-day, phone number, ss#, etc in pi
like this
http://www.angio.net/pi/piquery
13 years ago on Introduction
in example 2 of step 2 you show that the radius is 12 in. Don't you mean the diameter?
Reply 13 years ago on Introduction
You are correct. Thank you for pointing it out. I fixed the page. :-)
13 years ago on Introduction
I know it's not as precise, but 22/7 works for a close guesstimate.