# Separating number digits for readability
**URL:** https://boards.straightdope.com/t/separating-number-digits-for-readability/5436
**Category:** Factual Questions
**Created:** [December 17, 1999, 5:08pm UTC](https://boards.straightdope.com/t/separating-number-digits-for-readability/5436 "1999-12-17T17:08:00Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@JonF](https://boards.straightdope.com/u/JonF)
#### Post date: [December 17, 1999, 5:08pm UTC](https://boards.straightdope.com/t/separating-number-digits-for-readability/5436/1 "1999-12-17T17:08:00Z")
OK, teeming millions, here’s one about which I’ve always wondered.
All of the few cultures with which I’m familiar often write numbers with the integer portion separated by some character (comma, perios, or space) that group the number in sets of three digits starting at the right or the radix point.
Why three? Two seems silly, but four or five isn’t obviously wrong. And who decided on thre, anyway?
* * *
jrf
---
### Author:  [@pluto](https://boards.straightdope.com/u/pluto)
#### Post date: [December 17, 1999, 5:39pm UTC](https://boards.straightdope.com/t/separating-number-digits-for-readability/5436/2 "1999-12-17T17:39:00Z")
I think the writing merely reflects the words we use. We talk in terms of millions, billions and trillions, which have 6, 9 and 12 zeroes, respectively, after the “mantissa”. We can see at a glance that 6,000,000 is six million but it’s harder to recognize 600,0000. We have a word for three zeroes, a thousand, but not for four zeroes – we use ten thousand, a hybrid.
I’m not certain that the words came before the commas, but writing typically lags speech.
## I’ve also “read somewhere” that the largest grouping that a person can recognize without counting is five. Three is comfortably below that margin and still big enough to be useful. So it makes sense in that regard also.
“If ignorance were corn flakes, you’d be General Mills.”
Cecil Adams
_The Straight Dope_
---
### Author:  [@TheNerd](https://boards.straightdope.com/u/TheNerd)
#### Post date: [December 17, 1999, 8:12pm UTC](https://boards.straightdope.com/t/separating-number-digits-for-readability/5436/3 "1999-12-17T20:12:00Z")
and _I_ read that the number of things people can memorize easily is 7 +/- 2. (this had some bearing on phone numbers being 7 digits, grouped 3,4) So 3 is well within bounds. I’d prefer five.
I know that when I memorize big sequences like pi, I usually use groups of 5 or 6, for ease of memorization.
---
### Author:  [@JonF](https://boards.straightdope.com/u/JonF)
#### Post date: [December 20, 1999, 5:09pm UTC](https://boards.straightdope.com/t/separating-number-digits-for-readability/5436/4 "1999-12-20T17:09:00Z")
\> think the writing merely reflects the words \>we use. We talk in terms of millions, \>billions and trillions, which have 6, 9 and \>12 zeroes, respectively, after the \>“mantissa”. We can see at a glance that \>6,000,000 is six million but it’s harder to \>recognize 600,0000. We have a word for three \>zeroes, a thousand, but not for four zeroes \>-- we use ten thousand, a hybrid.
OK, I’ll buy that … then where did thousands and millions and billions come from? IMHO, the difficulty of recognizing 600,0000 is a matter of training.
---
### Author:  [@Boris\_B](https://boards.straightdope.com/u/Boris_B)
#### Post date: [December 20, 1999, 5:17pm UTC](https://boards.straightdope.com/t/separating-number-digits-for-readability/5436/5 "1999-12-20T17:17:00Z")
Off the subject, I know, but I have to point it out - there is a word in India, I don’t know if it’s Hindi or what - for one hundred thousand. Does anyone remember what it is? I want to say _bhat_ or _mhat_ … as in, “Mr. Singh went to the Taj Mahal and lost 3 bhat dollars before he realised that Atlantic City is not Agra”.
---
### Author:  [@pluto](https://boards.straightdope.com/u/pluto)
#### Post date: [December 20, 1999, 8:52pm UTC](https://boards.straightdope.com/t/separating-number-digits-for-readability/5436/6 "1999-12-20T20:52:00Z")
I have a nephew who is three years old and when you answer a question he always says, “Why?”
However, I agree that the answer I gave reflects the historical reason for the grouping of the digits rather than a logical reason. The logical reason is: “Just because.” (A useful answer for my nephew, too.)
I suppose it just happened that way. We have a word for one thousand so we don’t have to say “ten hundred”, but we don’t have a word for “ten thousand” (although apparently the Hindus do). Why this is so must be lost in the mists of antiquity.
My point was that if those are the words we have for numbers then it makes sense to write them the way we do. So, nephew dear, just because.