how to find the area of a cirle?


need to know the sq. in. of a given circle

12 Answers

  • 1 decade ago
    Favorite Answer

    How to Calculate the Area of a Circle

    A circle is one of the most interesting geometric shapes but is one of the more difficult ones to understand. Follow these steps to find the area of a circle. You will also learn how to find the area of a sector, which is a slice of a circle, similar to the shape of a slice of pie or pizza.

    Circumference Formula

    Find great deals and save! Compare products, prices & stores "I Cured My Yellow Teeth"

    Read the trick, discovered by a mom to turn yellow teeth white. Improve IT Service Levels

    Download Microsoft Virtualization Customer Cost Savings Whitepaper. Area Of A Circle

    Find more sources/options for Area Of A Circle

    Hide these ads

    Show Ads

    [edit] StepsArea of the circle

    Figure out the length of the radius. This may be as simple as dividing the diameter by 2.

    Note the formula. The formula for finding the area of a circle is: Multiply the radius by itself to square it.

    Multiply by pi.

    If the instructions say "leave in terms of pi", then just stick the pi onto your number.

    If the instructions say anything about rounding, replace pi with 3.14 or use your calculator's pi button.

    Here is an example:

    Occasionally you will see a circle inside of a square. The side length of the square matches the diameter of the circle.

    Occasionally you may see a square inside of a circle. The diagonal of the square is also the diameter of the circle.

    Finding the Area of a Sector

    Find out how big the sector is in terms of degrees. Unfortunately, there is no set way to do this. It will vary considerably, depending on what information is being supplied in the problem, and it is not possible to include a step-by-step process for every situation.

    Circleparts.JPGCreate a fraction that has: the degrees from the sector's central angle as the numerator, and 360° as the denominator.

    Take the fraction down to lowest terms.

    Figure out the radius of the circle.

    Find the area of the circle (see previous section).

    Multiply the fraction from step 3 with the area from step 5 OR divide the area by 360, then multiply by the # degrees in the partial circle.

    Here is an example:

    Generally speaking, you will not get a whole number coefficient for pi. If your radius is a multiple of 3, you will get some kind of cancellation between the fraction and the results of the ( )2, though. You will have to decide whether to: a) keep the fraction as a fraction and pi as pi, and cross-cancel as much as possible; or b) substitute 3.14 and finish the division completely.

    Measuring the Diameter of Round Objects

    Use a set of calipers, if possible, to measure across the object. This will give you the diameter.

    Use a flexible tape measure, like the ones used in sewing, to measure around the outside of the object. Be sure to measure it in centimeters. This will give you the circumference. Divide by 3.14 to find the diameter.

    With a cylindrical object, like a soup can, you can rest a ruler across the top of the can. Keep one end stationary while you rotate the other end. Keep rotating until you find the spot where the distance is the longest. This is the diameter.

    [edit] TipsIt is handy to have a calculator with you. A simple 4-function will do fine, but more complex calculators can store your measurements to use later. Or you might be able to use one on your computer.

    NOTE: 3.14 is only part of pi; there's really multiple numbers after the decimal point.

    This should be very helpful for you.

  • Anonymous
    1 decade ago

    The area of a circle is the number of square units inside that circle. If each square in the circle to the left has an area of 1 cm2, you could count the total number of squares to get the area of this circle. Thus, if there were a total of 28.26 squares, the area of this circle would be 28.26 cm2 However, it is easier to use one of the following formulas:

    A = Pi times r squared or A = Pi times r times r

  • spot a
    Lv 7
    1 decade ago

    Pi * r ^2

    r^2 is r squared or r * r

    Pi = 3.141593 approx

  • Anonymous
    1 decade ago


  • How do you think about the answers? You can sign in to vote the answer.
  • Anonymous
    1 decade ago

    pi r square

    22/7*square of radius

  • 1 decade ago

    pie r square

    pie = 22/7

    r = radius

  • Anonymous
    1 decade ago

    2 pie r r being radius

  • 1 decade ago

    r squared times pie

  • 1 decade ago

    A=pi*raidius * 2.

    A=pi * diameter

    Source(s): school
  • 1 decade ago

    pi(3.14)x radius to the 2nd power

Still have questions? Get your answers by asking now.