Why is an SMS just 160 characters?

The evolution of SMS

In the last few decades, the world has embraced an entirely new form of English. With fewer letters and more numbers than regular English, 'SMS language' or 'Textese' has taken the world by storm. But with such a high prevalence and everyday usage in our communications, it can be easy to forget why textese words such as 'TTYL', 'B4', and 'HRU' became littered throughout our everyday mobile communications.

Related article: The SMS turns 25 years old!

Advanced message stitching technology makes it easy to forget about the strict 160 character limit on SMS messages. While allowing our messages to become longer and less ridden with 'text talk', the limit still exists. In the past, every SMS that exceeded 160 characters was sent as two separate texts. Although now they appear to be sent as one, every SMS that exceeds this limit counts as two. SMS providers also charge SMS messages over 160 characters as if they were two.

Why 160 characters, you might ask? Why any restriction on the number of characters in an SMS whatsoever? And where did this absurd rule originate? This question has long plagued ardent SMS senders, and we answered it back in 2015. But we thought it was time to shed some light on this again. While poor documentation and various rumours have made finding the true origin of the 160 character limit a little bit messy, we've discovered the two most plausible answers. We'll let you decide for yourselves which one you think is correct.


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Theory one

The first story centres around a gentleman named Friedhelm Hillebrand. Friedhelm was a chairman of the Global Systems for Mobile Communications (a group that sets standards for the Global Mobile Market). Friedhelm had the important job to limit the number of characters a text message could contain.

Being the practical man he was, Friedhelm sat down with a typewriter and a cup of tea and started jotting down random sentences and questions. After writing a fair few, he counted the number of characters in each and found the average number of characters was (you guessed it) around 160.

Next, he took some postcards that he had received, counted all the letters in every sentence and found that the average amount was just under 150. Lastly, he analysed a number of the messages that came through on a Telex. Telex transmitters didn't have a character limit, so you might expect that each message's character count would vary. However, Friedhelm found that the character count was about the same as the postcards' messages. What a coincidence! Friedhelm took this research back to the board, and they decided to set the restriction that would make each SMS 160 characters.

Theory two

The second story is a little more technical and potentially more accurate. The organisation that Friedhelm worked for, the Global System for Mobile Communications (GSM), had cellular towers all over the place that were used to interpret calls through a system called 'packets'. These packets have limited space, and once the call information is taken out, is only left with 140 bytes.

SMS messages don't get their own packets when sent from tower to tower; they ride on the back of the call ones. So, it's believed that Friedhelm and his colleagues had a look at this remaining space and made an educated guess as to how many SMS characters they could squeeze in there.

In 1985, one character pretty much equated to one byte, so they decided that the character limit for an SMS should be 140. Since then, the GSM technology has improved, and they've been able to make each character less than one byte, meaning they could squeeze 160 characters into one SMS. Thus, the decision to limit each SMS to 160 characters.

Whether story one is correct, or the truth is in the second, or it's a combination of them both we may never know—but we sure do enjoy hearing the theories.

Which one do you believe?