| How to Calculate the Circumference of a Circle Sep 14th 2012, 02:00 Whether you're designing a project, doing craft work, or you need to know how much fencing you should buy to go around that hot tub in the backyard, knowing how to find circumference of a circle can come in handy. In this article, you'll learn just how and the promise is that it's easy as pie! Calculate the circumference using the diameter - Plug in the numbers. The formula for finding the circumference of a circle is this:
- C=πd. But what does that mean? There are three elements in this equation to figure out. These are:
- C, which is the circumference. This is the number you're looking for;
- d, which is the mathematical shorthand for diameter, and is the distance between the widest part of a circle, measured across the center; and finally
- π, or pi, which is pronounced "pie". Pi is an infinitely long number, but in this case, 3.14 will be close enough for fencing out the neighbors.
- Summarizing all that in words––the circumference of a circle is equal to the diameter of that circle, times pi.
- Try it out. Take a real world example of how you're going to use this formula to solve your neighbor problem.
- You have an 8-foot hot tub, as measured from one side to the other. You want to build a fence 6 feet out from it, all around. The diameter (d) of the tub is 8. Add 12 to that (remember—–6 feet all the way around), for a fence diameter of 20 feet.
- You know that π=3.14
- Grab your calculator, and enter 20 feet x 3.14=62.8 feet for the circumference. That's how much fencing you'll need to buy to get a little privacy.
Calculate the circumference using the radius - Know your radius. The radius (r) is the point from dead center in the middle of a circle, to the edge. It is exactly half the diameter, which will make this next formula easy:
- C= 2πr. You know already that C is the circumference, and that π = 3.14.
- Try it out. For this example, you're cutting out a decorative strip of paper to wrap around the edge of a pie you've just made.
- Measure from the center of the pie to the edge of the crust. (You don't want any crumbling). For this example, you find that the distance is 5 inches.
- Armed with this knowledge, you can now calculate:
- C=2 x 3.14 x 5, or 2 x 15.7, which just happens to equal 31.4.
Bonus points - calculating the area of a circle - Speaking of π. You may have heard the old joke, "Pi are squared? What? Pie are not square, pie are round!" That refers to the area of a circle, which is found by multiplying the the radius by itself, then multiplying that by 3.14. The formula is A=πr2.
- Therefore, in the second example above, the area of the pie is 78.5 inedible square inches.
- Consider buying an advanced calculator that already has π as one of the buttons. This will mean less typing for you and a more accurate answer because the π button produces an approximation to π that is much more accurate than 3.14.
Edit Warnings - Remember to always double-check your work because one mistake will set off all your data.
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