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How to Calculate Pi Download Article Calculate pi using the measurements of circle, an infinite series, Buffoon's Needle Problem, & more Reviewed by Grace Imson, MA
Last Updated: January 31, 2025 Fact Checked
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Using the Measurements of a Circle
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Using an Infinite Series
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Using Buffon's Needle Problem
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Using a Limit
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Using Arcsine Function/Inverse Sine Function
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Video
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Q&A
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Tips
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This article was reviewed by Grace Imson, MA. Grace Imson is a math teacher with over 40 years of teaching experience. Grace is currently a math instructor at the City College of San Francisco and was previously in the Math Department at Saint Louis University. She has taught math at the elementary, middle, high school, and college levels. She has an MA in Education, specializing in Administration and Supervision from Saint Louis University. There are 11 references cited in this article, which can be found at the bottom of the page. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 1,512,641 times.
Pi (π) is one of the most important and fascinating numbers in mathematics. Roughly 3.14, it is a constant that is used to calculate the circumference of a circle from that circle's radius or diameter.[1]XResearch source It is also an irrational number, which means that it can be calculated to an infinite number of decimal places without ever slipping into a repeating pattern.[2]XResearch source This makes it difficult, but not impossible, to calculate precisely.
Steps
Section 1 of 5:
Calculating Pi Using the Measurements of a Circle
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1 Make sure you are using a perfect circle. This method won't work with ellipses, ovals, or anything but a real circle. A circle is defined as all the points on a plane that are an equal distance from a single center point. The lids of jars are good household objects to use for this exercise. You should be able to calculate pi roughly because in order to get exact results of pi, you will need to have a very thin lead (or whatever you are using). Even the sharpest pencil graphite could be huge to have exact results.[3]XResearch source
2 Measure the circumference of a circle as accurately as you can. The circumference is the length that goes around the entire edge of the circle. Since the circumference is round, it can be difficult to measure (that's why pi is so important).[4]XResearch source
Lay a string over the circle as closely as you can. Mark the string off where it circles back around, and then measure the string length with a ruler.
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3 Measure the diameter of the circle. The diameter runs from one side of the circle to the other through the circle's center point.[5]XResearch source
4 Use the formula. The circumference of a circle is found with the formula C=πd=2πr. Thus, pi equals a circle's circumference divided by its diameter. Plug your numbers into a calculator: the result should be roughly 3.14.[6]XResearch source
5 Repeat this process with several different circles, and then average the results. This will give you more accurate results. Your measurements might not be perfect on any given circle, but over time they should average out to a pretty accurate calculation of pi.[7]XResearch source
Advertisement Section 2 of 5:
Calculating Pi Using an Infinite Series
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1 Use the Gregory-Leibniz series. Mathematicians have found several different mathematical series that, if carried out infinitely, will accurately calculate pi to a great number of decimal places. Some of these are so complex they require supercomputers to process them. One of the simplest, however, is the Gregory-Leibniz series.[8]XResearch source Though not very efficient, it will get closer and closer to pi with every iteration, accurately producing pi to five decimal places with 500,000 iterations. Here is the formula to apply.
Take 4 and subtract 4 divided by 3. Then add 4 divided by 5. Then subtract 4 divided by 7. Continue alternating between adding and subtracting fractions with a numerator of 4 and a denominator of each subsequent odd number. The more times you do this, the closer you will get to pi.
2 Try the Nilakantha series. This is another infinite series to calculate pi that is fairly easy to understand. While somewhat more complicated, it converges on pi much quicker than the Leibniz formula.[9]XResearch source
For this formula, take three and start alternating between adding and subtracting fractions with numerators of 4 and denominators that are the product of three consecutive integers which increase with every new iteration. Each subsequent fraction begins its set of integers with the highest one used in the previous fraction. Carry this out even a few times and the results get fairly close to pi.
Advertisement Section 3 of 5:
Calculating Pi
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Try this experiment to calculate pi by throwing hotdogs. Pi, it turns out, also has a place in an interesting thought experiment called Buffon's Needle Problem,[10]XResearch source which seeks to determine the likelihood that randomly tossed uniform elongated objects will land either between or crossing a series of parallel lines on the floor. It turns out that if the distance between the lines is the same as the length of the tossed objects, the number of times the objects land across the lines out of a large number of throws can be used to calculate pi. Check out the above wikiHow article link for a fun breakdown of this experiment using thrown food.
Scientists and mathematicians have not figured out a way to calculate pi exactly, since they have not been able to find a material so thin that it will work to find exact calculations.[11]XResearch source
Section 4 of 5:
Calculating Pi Using a Limit
Download Article
1 Pick a large number. The bigger the number, the more accurate your calculation will be.
2 Plug your number, which we'll call x, into this formula to calculate pi: x * sin(180 / x). For this to work, make sure your calculator is set to Degrees. The reason this is called a Limit is because the result of it is 'limited' to pi. As you increase your number x, the result will get closer and closer to the value of pi.
Advertisement Section 5 of 5:
Calculating Pi Using Arcsine Function/Inverse Sine Function
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1 Pick any number between -1 and 1. This is because the Arcsin function is undefined for arguments greater than 1 or less than -1.[12]XResearch source
2 Plug your number into the following formula, and the result will be roughly equal to pi.[13]XResearch source
π=｛arcsin[√(1 - x²)]+ abs[arcsin x]｝·2.
Arcsin refers to the inverse sine in radians
Sqrt is short for square root
Abs is short for absolute value
x^2 refers to an exponent, in this case, x squared.
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Question Is twenty two over seven equal to pi? Community Answer It is not precisely equal to pi. While it does look like pi at first (3.14285...), pi is 3.14159... It cannot be equal to pi because 3.14285 ends up repeating. Pi is an irrational number, meaning it goes on forever and does not repeat. Remember that irrational numbers are defined as "not being able to be written as a ratio between two numbers." 22/7 is a ratio of two numbers, so it cannot be exactly equal to pi. Thanks! We're glad this was helpful.Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 122 Helpful 360
Question How can I figure out pi as a fraction? Community Answer You can't. Pi cannot be a fraction because it is irrational. This means that it cannot be expressed as a ratio of two rational numbers. Pi is sometimes expressed as the fraction 22/7, but that is just an approximation. Thanks! We're glad this was helpful.Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 108 Helpful 293
Question What does the word irrational mean? Community Answer An irrational number is a number that cannot be expressed as a ratio of whole numbers (i.e., as a fraction). The root of the word 'irrational' is 'ratio', and the prefix 'ir' means 'not'. The word can have different meanings outside of math. Thanks! We're glad this was helpful.Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 71 Helpful 202
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Calculating pi can be fun and challenging, but doing so too deeply has diminishing returns. Astrophysicists say they only need to use pi to 39 decimal places in order to do cosmological calculations that are accurate to the size of an atom. Thanks Helpful 7 Not Helpful 0
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Reviewed by: Grace Imson, MA Math Teacher This article was reviewed by Grace Imson, MA. Grace Imson is a math teacher with over 40 years of teaching experience. Grace is currently a math instructor at the City College of San Francisco and was previously in the Math Department at Saint Louis University. She has taught math at the elementary, middle, high school, and college levels. She has an MA in Education, specializing in Administration and Supervision from Saint Louis University. This article has been viewed 1,512,641 times. 31 votes - 78% Co-authors: 64Updated: January 31, 2025 Views: 1,512,641 Categories: MathematicsArticle SummaryX
Pi is roughly 3.14, but it's actually an infinite number that never slips into a repeating pattern. If you want to calculate pi, first measure the circumference of a circle by wrapping a piece of string around the edge of it and then measuring the length of the string. Then, measure the diameter of the circle, which is the distance between one side and the other that runs through the center. Once you've got the circumference and diameter, plug them into the formula π=c/d, where "π" is pi, "c" is circumference, and "d" is diameter. Just divide the circumference by the diameter to calculate pi! To learn how to calculate pi using a limit or sine function, keep reading the article!Did this summary help you?YesNo
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Nov 24, 2020
"I was always the top math student in class, until I reached algebra. Now after reading your examples I realize that it was not me, but it was my teacher and the book we were using. Had I had this I could have gone so much further in school. Thank you."..." more
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Christi Carl
Nov 24, 2020
"I was always the top math student in class, until I reached algebra. Now after reading your examples I realize that it was not me, but it was my teacher and the book we were using. Had I had this I could have gone so much further in school. Thank you."..." more
John Tod
Jun 22, 2019
"I expected relatively easy formulae, but it is anything but easy. The article shows there are several ways to calculate pi. I read somewhere that NASA uses pi to 15 decimal places, which they consider "good enough.""..." more
Anonymous
Mar 18, 2018
"First time using. I understand what pi is. What an irrational number is. Excellent explanation for those who need it explained as simply as possible. I will continue to use this site."..." more
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Download Article Calculate pi using the measurements of circle, an infinite series, Buffoon's Needle Problem, & more Reviewed by Grace Imson, MA 
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Reviewed by: Grace Imson, MA Math Teacher This article was reviewed by Grace Imson, MA. Grace Imson is a math teacher with over 40 years of teaching experience. Grace is currently a math instructor at the City College of San Francisco and was previously in the Math Department at Saint Louis University. She has taught math at the elementary, middle, high school, and college levels. She has an MA in Education, specializing in Administration and Supervision from Saint Louis University. This article has been viewed 1,512,641 times. 31 votes - 78% Co-authors: 64 Updated: January 31, 2025 Views: 1,512,641 Categories: Mathematics Article SummaryX
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734 
1 Make sure you are using a perfect circle. This method won't work with ellipses, ovals, or anything but a real circle. A circle is defined as all the points on a plane that are an equal distance from a single center point. The lids of jars are good household objects to use for this exercise. You should be able to calculate pi roughly because in order to get exact results of pi, you will need to have a very thin lead (or whatever you are using). Even the sharpest pencil graphite could be huge to have exact results.[3] 
2 Measure the circumference of a circle as accurately as you can. The circumference is the length that goes around the entire edge of the circle. Since the circumference is round, it can be difficult to measure (that's why pi is so important).[4] 
3 Measure the diameter of the circle. The diameter runs from one side of the circle to the other through the circle's center point.[5] 
4 Use the formula. The circumference of a circle is found with the formula C=πd=2πr. Thus, pi equals a circle's circumference divided by its diameter. Plug your numbers into a calculator: the result should be roughly 3.14.[6] 
5 Repeat this process with several different circles, and then average the results. This will give you more accurate results. Your measurements might not be perfect on any given circle, but over time they should average out to a pretty accurate calculation of pi.[7] Advertisement 
1 Use the Gregory-Leibniz series. Mathematicians have found several different mathematical series that, if carried out infinitely, will accurately calculate pi to a great number of decimal places. Some of these are so complex they require supercomputers to process them. One of the simplest, however, is the Gregory-Leibniz series.[8] Though not very efficient, it will get closer and closer to pi with every iteration, accurately producing pi to five decimal places with 500,000 iterations. Here is the formula to apply. 
2 Try the Nilakantha series. This is another infinite series to calculate pi that is fairly easy to understand. While somewhat more complicated, it converges on pi much quicker than the Leibniz formula.[9] 
Try this experiment to calculate pi by throwing hotdogs. Pi, it turns out, also has a place in an interesting thought experiment called Buffon's Needle Problem,[10] which seeks to determine the likelihood that randomly tossed uniform elongated objects will land either between or crossing a series of parallel lines on the floor. It turns out that if the distance between the lines is the same as the length of the tossed objects, the number of times the objects land across the lines out of a large number of throws can be used to calculate pi. Check out the above wikiHow article link for a fun breakdown of this experiment using thrown food. 
1 Pick a large number. The bigger the number, the more accurate your calculation will be. 
2 Plug your number, which we'll call x, into this formula to calculate pi: x * sin(180 / x). For this to work, make sure your calculator is set to Degrees. The reason this is called a Limit is because the result of it is 'limited' to pi. As you increase your number x, the result will get closer and closer to the value of pi. Advertisement 
1 Pick any number between -1 and 1. This is because the Arcsin function is undefined for arguments greater than 1 or less than -1.[12] 
2 Plug your number into the following formula, and the result will be roughly equal to pi.[13] 
Community Answer It is not precisely equal to pi. While it does look like pi at first (3.14285...), pi is 3.14159... It cannot be equal to pi because 3.14285 ends up repeating. Pi is an irrational number, meaning it goes on forever and does not repeat. Remember that irrational numbers are defined as "not being able to be written as a ratio between two numbers." 22/7 is a ratio of two numbers, so it cannot be exactly equal to pi. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 122 Helpful 360 
Community Answer You can't. Pi cannot be a fraction because it is irrational. This means that it cannot be expressed as a ratio of two rational numbers. Pi is sometimes expressed as the fraction 22/7, but that is just an approximation. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 108 Helpful 293