What Are the Two Formulas Used to Find the Circumference of a Circle

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Need to know how to find the circumference of a circle? Can't remember the circumference formula? Don't sweat it—we've got you covered. If y'all know the diameter, simply plug information technology into this formula: C=πd. Were you given the radius, instead? No problem, just use this formula: C=2πr. Go on reading for everything you need to know about how to effigy out the circumference of a circle using either the diameter or the radius. We've even got a circumference calculator to make things easy.

1. ane

   Apply the formula C = πd to discover the circumference if you know the bore. In this equation, "C" represents the circumference of the circle, and "d" represents its diameter. That is to say, you lot can notice the circumference of a circle just by multiplying the bore past pi. Plugging π into your calculator volition give you its numerical value, which is a closer approximation of 3.14 or 22/seven.^[i]

   • Diameter means a directly line segment that passes through the center of the circle and has its endpoints on the sides of the circle.

2. 2

   Plug the given value of the diameter into the formula and solve. Check out the example problem below if you'd similar extra practice.^[two]

   • Case problem: You take a circle tub with a bore of 8 feet, and you want to build a white fence that creates a 6-foot wide space around the tub.
   • To find the circumference of the fence that has to be created, y'all should showtime notice the diameter of the tub and the fence which volition be 8 feet + six feet + 6 feet, which will business relationship for the entire diameter of the tub, plus the space between the tub and fence.
   • The diameter for your circular fence is eight + 6 + half-dozen, or 20 feet. Now plug it into the formula, plug π into your calculator for its numerical value, and solve for the circumference:
   • C = πd
   • C = π x 20
   • C = 62.viii feet

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1. 1

   Utilize the formula C = 2πr to discover the circumference using the radius. In this formula, "r" represents the radius of the circumvolve. Again, you lot tin can plug π into your calculator to become its numeral value, which is a closer approximation of iii.fourteen.^[iii]

   • A radius is any line segment that extends from the center of the circle and has its other endpoint on the border of the circle.
   • You might notice this is similar to the C = πd formula. That's because the radius is half as long as the diameter, so the diameter tin can be thought of as 2r.

2. 2

   Plug the given radius into the equation and solve. For this example, let'due south say you're cutting out a decorative strip of newspaper to wrap around the edge of a pie you've simply made. The radius of the pie is 5 inches. To find the circumference that you lot need, just plug the radius into the equation:^[4]

   • C = 2πr
   • C = 2π x 5
   • C = 10π
   • C = 31.4 inches

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Effort it yourself! Enter a value to calculate circumference.

C = 2π r

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• Question

  What is the perimeter of a circle?

  

  This answer was written past i of our trained squad of researchers who validated it for accuracy and comprehensiveness.

  

  wikiHow Staff Editor

  Staff Answer

  The perimeter of a circumvolve is the aforementioned as its circumference, the distance around information technology. The term "perimeter" refers to the altitude effectually any airtight shape, and "circumference" applies specifically to a circle or arc.

• Question

  What'due south the departure between the circumference and the diameter?

  

  This respond was written by ane of our trained squad of researchers who validated it for accurateness and comprehensiveness.

  

  wikiHow Staff Editor

  Staff Reply

  The bore is the length of a straight line fatigued through the centre of a circle from 1 side to the other. The circumference is the length all the mode effectually the outside of the circle.

• Question

  What is a circumference?

  

  Circumference is the altitude around the perimeter of a circle. It is calculated past multiplying the distance beyond the center (diameter) by Pi (3.1416).

• Question

  If I know the radius of a circle, how I can observe the circumference?

  

  Double the radius to get the diameter. Then multiply by pi to get the circumference.

• Question

  How practice I find the radius when I go the circumference?

  

  The circumference = π 10 the diameter of the circumvolve (Pi multiplied by the bore of the circle). Only divide the circumference by π and you volition take the length of the diameter. The diameter is merely the radius times two, so divide the diameter by two and yous will have the radius of the circumvolve!

• Question

  How tin I find the diameter of the circle, in one case I know the circumference?

  

  Circumference (C) = pi * diameter(d). To get the diameter of a circle take the circumference (C) and carve up information technology by pi (three.14).

• Question

  How do I observe the area of a circle when simply given the circumference?

  

  Split up the circumference by pi. That's the diameter. Divide past 2. That's the radius. Square the radius, and multiply past pi. That's the surface area.

• Question

  What is the formula used to calculate diameter?

  

  The diameter is twice the radius. The circumference is diameter x pi, or two x radius x pi.

• Question

  How do I change the mixed number into radius?

  

  If your radius is a mixed number, turn the number into an improper fraction. To do this, simply multiply the whole number part past the denominator and add that number to the numerator. The denominator should remain the same throughout the process. Yous tin then use the improper fraction in your formula.

• Question

  What is the answer of the circumference of a circle?

  

  The answer depends on your number. For instance, pie or three.14 is multiplied with your number which is the diameter or radius.

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VideoRead Video Transcript

• Consider buying a scientific or graphing reckoner that already has π as i of the buttons. This volition mean less typing for yous and a more accurate answer because the π push button produces an approximation to π that is much more accurate than 3.14.

• Remember: some worksheets volition ask to supersede pi with a subside, such equally 3.fourteen or 22/7.

• To find circumference from the diameter, just multiply pi by the bore.

• The radius is ever going to exist half of the diameter.^[5]

Thanks for submitting a tip for review!

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• Have your time. Remember the old adage—measure twice, cut once.

• If you are stuck, ask a friend, family fellow member, or teacher for help.

• Call up to always double-check your piece of work because i error will set off all your data.

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Commodity Summary X

To calculate the circumference of a circle, apply the formula C = πd, where "C" is the circumference, "d" is the diameter, and π is three.14. If you have the radius instead of the diameter, multiply information technology past 2 to go the diameter. Y'all tin besides use the formula for circumference of a circumvolve using radius, which is C = 2πr. To meet bodily examples of the circumference of a circumvolve being calculated, read the article!

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