If You Know the Radius How Do You Find the Circumference

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Whether you lot're solving a math problem for school, making crafts, or putting fencing around your chiliad, knowing how to calculate the circumference of a circle volition come in handy in a variety of circle-related problems. We'll teach y'all the key circumference formulas you need to figure out the circumference of a circle when you lot know either the diameter or radius.

1. one

   Use the formula C = πd to find the circumference if you lot know the bore. In this equation, "C" represents the circumference of the circle, and "d" represents its diameter. That is to say, you can observe the circumference of a circle merely past multiplying the diameter by pi. Plugging π into your calculator will requite y'all its numerical value, which is a closer approximation of iii.14 or 22/7.^[1]

   • Diameter means a directly line segment that passes through the eye 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 trouble below if y'all'd like extra practice.^[2]

   • Example problem: You lot have a circumvolve tub with a diameter of viii feet, and yous want to build a white argue that creates a 6-foot wide infinite around the tub.
   • To notice the circumference of the fence that has to be created, you should kickoff find the diameter of the tub and the fence which will exist viii feet + half dozen anxiety + 6 anxiety, which volition account for the entire diameter of the tub, plus the space between the tub and fence.
   • The diameter for your circular fence is 8 + vi + half dozen, or xx feet. At present 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 = 62.8 feet

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1. 1

   Use the formula C = 2πr to discover the circumference using the radius. In this formula, "r" represents the radius of the circle. Again, you tin can plug π into your calculator to get its numeral value, which is a closer approximation of iii.14.^[iii]

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

2. 2

   Plug the given radius into the equation and solve. For this instance, let's say y'all're cut out a decorative strip of paper to wrap around the edge of a pie you've just made. The radius of the pie is five inches. To detect the circumference that you need, simply plug the radius into the equation:^[four]

   • C = 2πr
   • C = 2π x 5
   • C = 10π
   • C = 31.iv inches

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Effort it yourself! Enter a value to summate circumference.

C = 2π r

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• Question

  What is the perimeter of a circle?

  

  This answer was written by 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 same as its circumference, the distance effectually it. The term "perimeter" refers to the distance effectually whatever closed shape, and "circumference" applies specifically to a circle or arc.

• Question

  What's the deviation between the circumference and the diameter?

  

  This reply was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.

  

  wikiHow Staff Editor

  Staff Answer

  The diameter is the length of a straight line fatigued through the center of a circumvolve from 1 side to the other. The circumference is the length all the way effectually the outside of the circle.

• Question

  What is a circumference?

  

  Circumference is the distance around the perimeter of a circle. Information technology is calculated by multiplying the altitude beyond the eye (diameter) by Pi (3.1416).

• Question

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

  

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

• Question

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

  

  The circumference = π x the diameter of the circle (Pi multiplied past the diameter of the circle). Simply dissever the circumference by π and y'all will have the length of the bore. The diameter is merely the radius times two, and so divide the diameter by two and you will have the radius of the circle!

• Question

  How tin I find the bore of the circle, once I know the circumference?

  

  Circumference (C) = pi * diameter(d). To get the bore of a circumvolve accept the circumference (C) and divide information technology past pi (three.14).

• Question

  How do I notice the area of a circumvolve when simply given the circumference?

  

  Separate the circumference past pi. That's the diameter. Divide by ii. That's the radius. Square the radius, and multiply by pi. That'south the expanse.

• Question

  What is the formula used to summate diameter?

  

  The bore is twice the radius. The circumference is diameter x pi, or 2 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 by the denominator and add that number to the numerator. The denominator should remain the aforementioned throughout the procedure. Yous can and so 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 calculator that already has π as one of the buttons. This will hateful less typing for y'all and a more accurate respond because the π button produces an approximation to π that is much more accurate than three.fourteen.

• Recollect: some worksheets will ask to supervene upon pi with a subside, such every bit 3.14 or 22/7.

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

• The radius is always 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, enquire a friend, family member, or teacher for help.

• Remember to e'er double-cheque your work because one error will set off all your information.

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About This Article

Article Summary X

To calculate the circumference of a circumvolve, utilise the formula C = πd, where "C" is the circumference, "d" is the diameter, and π is 3.14. If you have the radius instead of the diameter, multiply it by 2 to get the diameter. You can as well use the formula for circumference of a circumvolve using radius, which is C = 2πr. To see bodily examples of the circumference of a circle being calculated, read the commodity!

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