How to Deduce Circumference of Circle

The circumference of a circle is the distance all the way around a circle. If you measure the circumference and divide it by the circle's diameter (the distance across the center of the circle, from one side to another), you will always get a constant called "pi." Pi is often written as "π" and is equal to approximately 3.14. You can use this special relationship to deduce the circumference of a circle by using the formula C=πd. C is the circumference, d is the diameter and π is pi. You may also be given the radius (half of the diameter) in a word problem.

Instructions

1. Read the question carefully to make sure you understand if you are being given the radius or diameter. For example, in the question, "Find the circumference of a circle if the radius is 10cm," you are given the radius, not the diameter.

2. Multiply the radius by 2 to get the diameter. For example, using the above example:
   2 * 10 cm radius = 20 cm diameter.
   If you are given the diameter in the question, do not multiply by two. Just skip to Step 3.

3. Multiply the diameter by pi (3.14). For example:
   20 cm * 3.14 = 62.8 cm: the circumference.

Tips & Warnings

• The value of pi has more than a trillion decimal places. For most problems, two decimal places (3.14) will give you a reasonable answer. Teachers may want you to be more accurate with your answer, so check with them about how many decimal places they want you to compute.