# CKDextHavn reply to 'is pi an exact number' **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [August 2, 2002, 11:32pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098 "2002-08-02T23:32:37Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![robot-penguin](https://avatars.discourse-cdn.com/v4/letter/r/ea666f/32.png) [@robot-penguin](https://boards.straightdope.com/u/robot-penguin)\ **Post date:** [August 2, 2002, 11:32pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/1 "2002-08-02T23:32:37Z")
In CKDextHavn’s over-complicated explanation of the definition of pi it was neglected to mention that pi is not an exact number NOR an infinitum. Pi can be calculated with the simple expression of > [@](#): > > 22÷7 which, on simple calculators, gives the answer > [@](#): > > 3.1428571428571428571428571428571 . ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [August 2, 2002, 11:57pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/2 "2002-08-02T23:57:46Z")
You’re referring to [this Staff Report](http://www.straightdope.com/mailbag/mpi.html) by CKDextHavn. I’m afraid you’ve misunderstood **Dex**. Pi most certainly can _not_ be calculated as 22/7. True, it’s not a bad estimate, since it’s easy to remember, but the first few digits of pi are: 3.14159265358979323846264338327950… and so forth. Close to 3.1428571428571428571428571428571…, but not the same number at all. [This page](http://www.cecm.sfu.ca/projects/ISC/dataB/isc/C/pi10000.txt)’ll give you the first 10,000 digits of pi, and you can go [here](http://www.cecm.sfu.ca/pi/pi.html) if you want to know more about the number. Bottom line: pi is irrational and, if you write it out, the digits do not repeat. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [August 3, 2002, 7:08am UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/3 "2002-08-03T07:08:13Z")
Actually, 22/7 isn’t even that good an approximation of pi. You’d be better off using 3.142. pi = 3.14159… which, rounded to 3rd decimal place is 3.142 22/7 = 3.14285… which, rounded to 3rd decimal place is 3.14_3_ Heck, it’s not that hard to memorize 3.14159. Use _that_ instead of 22/7. By the way, **robot-penguin** , where did you learn that? I think perhaps you misheard, unless the person you learned it from was the mistaken one. ---
**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\ **Post date:** [August 3, 2002, 12:15pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/4 "2002-08-03T12:15:46Z")
Well, there’s always the argument that pi is exactly 3, because the Bible says so. There is a reference, I think somewhere in Kings, to a circular something or other that is 10 cubits wide and 30 cubits around. Welcome to the Straight Dope Message Boards, penguin, we’re glad to have you here… but you are misremembering. 22/7 is a estimate of pi that is usable for many purposes, but is not the same as pi, as already noted by zut and Irishman. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [August 3, 2002, 12:33pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/5 "2002-08-03T12:33:37Z")
I’m working on yet another Staff Report on pi right now, and I find it quite amazing the number of reasonable and intelligent people who are absolutely convinced that [symbol]p[/symbol]=22/7 exactly. I blame the schools. Then again, I blame the schools for pretty much everything. ---
**Author:** ![lel](https://avatars.discourse-cdn.com/v4/letter/l/8797f3/32.png) [@lel](https://boards.straightdope.com/u/lel)\ **Post date:** [August 3, 2002, 10:49pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/6 "2002-08-03T22:49:22Z")
Did anyone else learn to approximate pi as 355/113? Just like any approximation, it’s not exact, but it is closer than 22/7. 22/7: 3.1428571428… 355/113: 3.1415929203… Pi: 3.1415926535… Also, [here](http://bible.gospelcom.net/cgi-bin/bible?passage=1KGS+7:23&language=english&version=KJV&showfn=on&showxref=on) is where the Bible mentions the round molten sea that is 10 cubits wide and 30 around. ---
**Author:** ![waterj2](https://avatars.discourse-cdn.com/v4/letter/w/858c86/32.png) [@waterj2](https://boards.straightdope.com/u/waterj2)\ **Post date:** [August 4, 2002, 2:00am UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/7 "2002-08-04T02:00:03Z")
How would 355/113 be any easier than 3.141593? I guess you can save one digit of memory space, but it would take longer to use in most aspects, such as entering it into a calculator. ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [August 4, 2002, 10:45am UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/8 "2002-08-04T10:45:19Z")
I personally like to use 3000[sup]1/10[/sup] + 75/82. I think that’s pretty easy. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 5, 2002, 4:11am UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/9 "2002-08-05T04:11:10Z")
> [@](#): > > There is a reference, I think somewhere in Kings, to a circular something or other that is 10 cubits wide and 30 cubits around. What’s more, it’s actually possible that those measurements are exactly and precisely correct. The object in question is bowl-shaped, so if measurements are restricted to the surface of the bowl, then we’re in spherical geometry, and [symbol]p[/symbol] is less than the Euclidian value. It is possible for a circle in spherical geometry to have diameter of exactly 10 cubits and circumference of exactly 30 cubits. ---
**Author:** ![MEBuckner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mebuckner/32/2896_2.png) [@MEBuckner](https://boards.straightdope.com/u/MEBuckner)\ **Post date:** [August 5, 2002, 4:40am UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/10 "2002-08-05T04:40:29Z")
> [@](#): > > \*Originally posted by bibliophage \* > I blame the schools. Then again, I blame the schools for pretty much everything. Hmmm…You know, Oswald was in a _school_ book depository. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [August 5, 2002, 11:10am UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/11 "2002-08-05T11:10:29Z")
I do remember hearing somewhere in grade school that 22/7 was an approximate, but I always found it easier to just memorize 3.14 (way back in grade school, 3 sig digits was ample). Later I just increased that to 3.14159. For most calculations, I could always use the pi button on the calculator, anyway. 😉 ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [August 5, 2002, 11:03pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/12 "2002-08-05T23:03:05Z")
To answer another aspect of the OP, there is no such thing as an “inexact” number when one is talking about reals. There are numbers which have no finite decimal expansion, but they’re still “exact” (I’m not sure that that’s an actual mathematical term–it’s not listed at mathworld, at least. Dex?). ---
**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\ **Post date:** [August 6, 2002, 12:03pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/13 "2002-08-06T12:03:41Z")
I don’t disagree, ultrafilter, there’s technically no such thing as an “exact” number vs an “inexact” number. But I thought I knew what the OP meant, sort of, using common English rather than mathematics as the language of communication. Thus, 3.14159 is an certainly an “exact” number – it is different from 3.141592 or 3.14158, for instance. But it is not “exactly” pi. That is, pi is not “exact” in the sense that pi is an irrational, so that you can never write down all of its decimals, hence whenever you stop, you will have an “inexact” approximation. There is another possible sense of “inexact.” The Real Numbers are, after all, a theoretical construct. Try though you will, you cannot construct a line that is “exactly” 1 cm long. Measurement is all inexact or approximate, having a margin of error. Thus, the exact/inexact can be used to distinguish between the real world and the math-theoretic world. ---
**Author:** ![h.sapiens](https://avatars.discourse-cdn.com/v4/letter/h/e0b2c6/32.png) [@h.sapiens](https://boards.straightdope.com/u/h.sapiens)\ **Post date:** [August 6, 2002, 12:39pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/14 "2002-08-06T12:39:40Z")
If inside a circle a line, Hits the center and goes spine-to-spine, If the line’s length is d, The circumference will be: d x 3.14159 I didn’t write this, and I can’t remember where I read it, but it’s nifty, eh? ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [August 6, 2002, 5:36pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/15 "2002-08-06T17:36:59Z")
Now I – even I – would celebrate In rhymes inept the great Immortal Syracusan rivaled nevermore, Who by his wondrous lore, Untold us before, Made the way straight How to circles mensurate. – Edouard Prevost ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 7, 2002, 7:19am UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/16 "2002-08-07T07:19:49Z")
Am I the only one who just finds it easiest to approximate it as 3.14159265358979323846? A simpler mnemnonic, by the way, is “May I have a large container of coffee?”. It’s fortunate for the mnemonicizers that it happens to take a while for a zero to show up. ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [August 7, 2002, 5:04pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/17 "2002-08-07T17:04:58Z")
I say, why approximate? Just leave your answer in terms of _pi_. For crying out loud, we’re not _engineers_. ---
**Author:** ![aerodave](https://avatars.discourse-cdn.com/v4/letter/a/f08c70/32.png) [@aerodave](https://boards.straightdope.com/u/aerodave)\ **Post date:** [August 7, 2002, 10:14pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/18 "2002-08-07T22:14:51Z")
> [@](#): > > \*Originally posted by Achernar \* > \*\*I say, why approximate? Just leave your answer in terms of _pi_. For crying out loud, we’re not _engineers_. \*\* Pardon me…but some of us _are_ engineers. 😉 ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [August 8, 2002, 9:54am UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/19 "2002-08-08T09:54:37Z")
Well, geez, if you’re an engineer, then [pi = 3](http://www.straightdope.com/classics/a3_341.html) should be good enough for you, no? 😉 What’s worse, I notice that both **John W. Kennedy** ’s mnemonic and **Chronos** ’s mnemonic round the wrong way. Unless **Chronos** counts the question mark. 🙂 ---
**Author:** ![Tom\_Arctus](https://avatars.discourse-cdn.com/v4/letter/t/71c47a/32.png) [@Tom\_Arctus](https://boards.straightdope.com/u/Tom_Arctus)\ **Post date:** [August 8, 2002, 5:25pm UTC](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098/20 "2002-08-08T17:25:29Z")
> [@](#): > > \*Originally posted by Chronos \* > \*\*What’s more, it’s actually possible that those measurements [from the Christian Bible] are exactly and precisely correct . . . It is possible for a circle in spherical geometry to have diameter of exactly 10 cubits and circumference of exactly 30 cubits. \*\* I’m sorry, I don’t follow you. Are we talking about a circle that also happens to lie on the surface of a sphere in a three-dimensional Euclidian space? Because if we are it seems to me it would have to also lie in some plane in that space and conform to the other requirement of a circle, that of having all its points equidistant from its center. So its circumference would still have to be pi times its diameter, not exactly three times its diameter. There’s no way that I know of to deform a circle as defined above in Euclidian or any other space so that the ratio of its circumference to its diameter conforms to the Biblical passage you cite. I admit that yours is a more sophisticated argument, if only on the surface, than the more common one that the Bible writers were citing measurements of the outside diameter of a thick wall and its inside circumference or suchlike. But the bottom line is that the Christian Bible is not a mathematics text; the value of pi or its deriviation was unknown to its authors; they apparently had no other earthly or divine source for the correct information; and so 3 was close enough to pi for them. I suppose I could be wrong as I never really got into non-Euclidian geometries, but for now I’d have to bet that I’m not wrong. [Next page](https://boards.straightdope.com/t/ckdexthavn-reply-to-is-pi-an-exact-number/122098.md?page=2)