Whether as a requirement for a class, or in order to successfully complete a project around your house, have you ever needed to accurately measure the distance around a circle? Otherwise known as a circle's "circumference", measuring the distance around a circle doesn't have to be a painstakingly difficult process and leaning how to measure a circumference of a circle can have far ranging practical applications, as well.

Follow the steps in this Info Barrel article in order to accurately measure the circumference of a circle by using either the diameter or the radius of a circle. If the circle that you would like to measure the circumference of is a perfect circle, you can still gain an estimate of its circumference by following the steps in this article. Unfortunately, the less a circle resembles of a perfect circle, the less accurate your circumference measurement will be.

Things You Will Need

a Piece of Paper
a Pen
a Calculator

Step 1

More oftentimes than not, the circle that you will want to measure the distance around wont be a perfect circle. This simply means that each point that forms the actual circle, in a perfect circle, will be the same exact distance away from the center. While we would all love it to be the case, most circles wont be perfect circles. With this in mind, it is important that you first determine what you would like to measure.

Step 2

Every perfect circle will have an exact center point within it. If you are not measuring a perfect circle, you will have to first best estimate the center of the circle. Bear in mind that, when you estimate the center of a circle, every other measurement has the potential to be skewed from its true circumference. In a perfect circle, rather than taking a measuring tape and measure the entire outside perimeter of a circle, determining a circle's exact center point and diameter will help you to determine the circumference of the circle you are measuring.

Unlike a radius, a diameter cuts entirely through a circle from one side to another side while going through the center point. A diameter, by its very definition, will cut the circle into two semi-circles. For circles that are not perfect in nature, your diameter will have to be an estimation just like your center point. Dependent upon how much your circle deviates from perfect will determine how much accuracy in sacrificed in your measurement. If you require a highly accurate measurement, on a less-than-perfect circle, then you will have to reconsider estimating throughout this process.

Step 3

Dependent upon what you need to measure, it may be unrealistic to obtain a full diameter on your circle. By their very nature, circles can be very tiny or very large. If you must measure a circle that spans for miles, in order to spare you time you should consider measuring a radius of your circle as opposed to a diameter. Because a radius simply extends from a circle's center point to any point on the circle, a radius will essentially be 1/2 of your diameter measurement. For example, if you have a diameter length of 10 meters, your radius would be 5 meters. Likewise, if you had a radius of 5 meters, your diameter would be 10 meters. (diameter = radius x 2)

If you use a radius measurement, on an imperfect circle, you can expect to receive a circumference that is less accurate than had you used a diameter measurement. Dependent upon the circle you are measuring, you will have to determine whether it would be in your best interest to use a diameter or a radius to gain a circumference.

Step 4

"Pi" is a value that is known as a mathematical constant. In conjunction with either your obtained diameter or radius, you will need to use "pi" in order to determine your circle's circumference. No matter what the size of your circle is, whether it be massive or tiny in scale, "pi" will always remain the same as an expressed ratio between a circumference of a circle and it's diameter. Even though "pi's" value will extend for infinity, it is typically rounded off to 3.14. Of course, if your measurement requires incredible accuracy, the further 'places' you go out beyond "4", the more accurate your measurement will be.

Step 5

The formula for circumference will require both the "Pi" value as well as your diameter measurement. When written out, your formula will look like this: C=Pi x d. Remember that if you used a radius, you would have to multiply your radius by 2 in order to get the diameter measurement that you will place into your formula.

As you can see from this Info Barrel article, measuring a circle's circumference isn't overly difficult. Like any other formula, in order to achieve the right answer, you will need to inject the correct information into the given formula. While your "Pi" value will always be constant, your diameter or radius will actually require measurement or an estimation. If you are attempting to find the circumference of a perfect circle, your measurement will be much more accurate than had you just estimated. In certain situations, however, it may be impractical to measure either a diameter or a radius, especially with limited tools and resources.

The formula for circumference can help assist you to greatly expedite making this determination. The alternative option, however, would be to actually measure the entire circle around. In some situations, like measuring a marathon track, this may be completely impractical and could be better done with an accurate (or estimated) diameter or radius.

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