2012-07-02

Text message lengths

Several text messaging technologies impose character limits on messages. This blog post describes those limits and their advantages.

The advantages of a maximum message length

Historically, the lengths of text messages were usually limited due to technical reasons. For example, the data packets holding SMS messages only had room for 160 characters (see below). Now that those technical reasons matter less, people are recognizing that limits have other advantages. For example, Twitter messages could easily be longer, but their brevity encourages people to write things publicly that they wouldn’t via formats with longer messages such as blogs. Hence, Twitter gives us insights that other formats don’t. Twitter’s limit also improves quality: There is no opportunity for rambling and messages are generally more polished, because there is less text to polish and because one often has to spend considerable time to edit content down to 140 characters. Every word matters, so more thought goes into which words to include and which ones to leave out. The following quote (via Shortmail) expresses nicely that brevity takes work and is usually desirable.
I would have written a shorter letter, but I did not have the time.
Blaise Pascal

Text messaging technologies

The following are three text messaging technologies and their length limits.

Short Message Service (SMS): 160 characters

The key original idea of SMS was to make messages short and to use the control protocol to deliver them. A cell phone and the network periodically exchange data packets on a secondary channel, for control tasks (e.g., to enable roaming from one cell tower to another or to initiate a call). When none of these tasks need to be performed, there is unused space in such packets. That is where the SMS data is squeezed in. When SMS was first publicly available in the early 1990s, this trick was important, because it made messages cheap to deliver. The maximum size of an SMS message is dictated by the size of control packets. It was originally 140 bytes or 160 7-bit characters. Now there are ways to write longer messages.

Twitter: 140 characters

When Twitter started, an important goal was that tweets could be sent from anywhere. Back in 2006, internet-enabled phones were not yet very common (as a reference point, the iPhone was released in mid 2007). Hence, Twitter supported creating tweets via SMS. Initially, there was no character limit for messages, which caused problems:
Messages longer than 160 characters (the common SMS carrier limit) were split into multiple texts and delivered (somewhat) sequentially. There were other bugs, and a mounting SMS bill. The team decided to place a limit on the number of characters that would go out via SMS for each post. They settled on 140, in order to leave room for the username and the colon in front of the message.


[“How Twitter Was Born” by Dom Sagolla for 140 Characters]

Shortmail: 500 characters

Shortmail is a new email service that imposes a length limit for messages. It has been called “Twitter for email”. They decided on a limit of 500 characters.

What are good character limits?

There are three length categories for messages: Short (SMS, Twitter), medium (most email) and long (articles, blog posts). It doesn’t make sense to limit long messages, because that format is usually chosen to enable comprehensive content. But what are good limits for short and medium messages?

SMS message length

The SMS inventors Friedhelm Hillebrand and colleagues wondered whether 160 characters would be enough for meaningful communication:
Having zero market research, they based their initial assumptions on two “convincing arguments,” Hillebrand said.

For one, they found that postcards often contained fewer than 150 characters.

Second, they analyzed a set of messages sent through Telex, a then-prevalent telegraphy network for business professionals. Despite not having a technical limitation, Hillebrand said, Telex transmissions were usually about the same length as postcards.

Just look at your average e-mail today, he noted. Many can be summed up in the subject line, and the rest often contains just a line or two of text asking for a favor or updating about a particular project.


[“Why text messages are limited to 160 characters” by Mark Milian for L.A. Times]

Tweet length

I’m fairly happy with Twitter’s 140 character limit. Sometimes one tweet isn’t enough to express something, especially when commenting on another tweet while quoting it. But I never need more than two tweets, so 280 characters should be enough for all short-message purposes.

Email message length

Quoting the Shortmail FAQ:
Why 500 characters? We came up with the number after working with one of our other products, Replyz. We found that it is long enough to allow people to express a complex idea, but not so long as things get wordy. We think it will emerge as a standard length for “short” email.
Emails rarely comprise more than two paragraphs. The article “Plain Paragraph Length” (by Nirmaldasan for Readability Monitor) mentions paragraphs in business letters having 60 words. Assuming an average word length of six characters (including a space), we get 360 characters per paragraph. That makes Shortmail’s 500 character limit seem like a good choice. It would be interesting to examine a large corpus of email messages. A sweet spot should be easily detectable by graphing lengths, with rambling messages making up the long tail on one side.

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