Iris Classon
Iris Classon - In Love with Code

Stupid Question 183: Why are SMS 160 characters and tweets 140?

[To celebrate my first year of programming I will ask a ‘stupid’ questions daily on my blog for a year, to make sure I learn at least 365 new things during my second year as a developer]

Why are SMS 160 characters and tweets 140?

Last Saturday I was eating dinner at a friend’s house, and we had a small room of nerds. Two developers, one IT-Pro and an engineer. Somehow we started talking about SMS, and why the character constraint. We couldn’t quite agree on the reason for why it’s just 160 characters. Let’s get to the bottom of this.
While there areplenty of articles onlineclaiming that the reason was this one guy, Friedhelm Hillebrand , did some random research on written communication and came to the conclusion that 160 would do. And then it became the standard. Really?

This is how I understood the 160 character limit after some research:
Friedhelm Hillebrand did indeed, together with other researchers, study what a meaningfull limit would be for written (but short) communication- to test whether or not people would find the service useful if limited by the number of characters. Positive that it would work, the limit was then set to a max of 160 characters transmission size. AS for why, and please correct me if my information is wrong, is because the current hardware of the GSM mobile handset devices at that time was limited to 140.
Due to the popularity of SMS several services have followed the model, such as Twitter- where a ‘tweet’ is limited to 140 characters, as the remaining 20 are for the username.
Now, I would LOVE to get some information about this- so if you know anything about this topic please share,- let’s get all the facts down once and for all :)


Leave a comment (via email)
Marcel VeldhuiMarcel Veldhuizenzen
5/1/2013 4:51:38 AM
As far as I recall, 140 bytes was the maximum amount of data that could be contained into a single message/packet for the protocols used at the time when SMS was defined. 140 bytes translates to 160 7-bit characters.

I have no idea if those packet sizes are still valid with current 3G and 4G standards however. 
5/1/2013 4:53:37 AM
I used to work on an SMS back-end engine, so here goes: texts are actually 140 bytes long (I doubt any psychology research went into that, SMS was initially meant to be a diagnostic tool for engineers). The GSM character encoding is 7 bits, so you can get 140*8/7 = 160 characters into an SMS :-).

Here's the character set, from 0x00 to 0x7F (i.e. 128 characters): 
5/1/2013 4:53:46 AM
I remember reading an interview with Jack Dorsey where he discussed the reasoning for Twitters 140 character limit was originally you would send Tweets via text message. So then 140 characters were for the message and 20 for the username! But due to the rise in mobile internet that model never became prevalent. 
Robert MacLean
5/1/2013 5:19:07 AM
Twitter has a relation to SMS, but not in the way you implied. The origin of the company was to build a group SMS chat system (i.e. you send to Twitter, they relay to a group). They reserved 20 for tracking IDs so that the system could identify what conversation & participates the message is for. However they pivoted the business at one point when they found people using the beta which was just web based were loving it and the idea original was abandoned. 
Jan Kok
5/2/2013 8:53:31 AM
I found a nice article about the history of SMS at: 
David Hamilton
5/31/2013 6:03:29 PM
I believe that CDMA (first US networks for SMS) networks could only cope with 140 characters, however, as mentioned above, GSM due to its encoding could do 160. Twitter coming from over in the US would have gone with 140 due to the limitations of the networks 

Last modified on 2013-04-30