The number of characters in an SMS text message

Nerd Insider By Nerd Insider, 7th Dec 2012 | Follow this author | RSS Feed
Posted in Wikinut>Guides>Technology>Mobile Phones

An explanation of the maximum number of characters which can be used in an SMS message and the impact of different encoding alphabets.

Introduction

We all know that the maximum number of characters in a tweet is 140, but if you're anything like me you'll have sent countless text messages over the years while having no clue to their character limits. All I knew was that my phone would start a little countdown when I was nearing the maximum.

I was writing about SMS messaging on Skype recently when this gap in my knowledge occurred to me, so I had a quick root around the internet to find the answer, and it was more complicated than I expected.

The Character Limits and Encoding Character Sets

It turns that there are different character limits depending on the language you are using and whether or not you're using any special characters. There are three different alphabets (or character sets) which can be used to encode an SMS: the GSM 7-bit alphabet, the 8-bit data alphabet (IA5/ASCII) and the 18-bit UCS-2 alphabet (Unicode).

Each has a different character limit:

GSM 7-bit: 160 characters

This character set is made up of mostly the characters derived from the Latin alphabet, numbers, basic mathematical symbols, punctuation and a several special symbols. The majority of Western European languages use characters derived from the Latin alphabet. So if you write a message in English, French, German, Italian etc. the GSM 7-bit alphabet will be sufficient. The character set includes letters with diaeresis, graves, tildes, and acutes e.g. ö, à, ñ and é.

National Language Shift Tables have been created which allow several other alphabets to be encoded with GSM 7-bit. However the character limit for these alphabets is 155; the other 5 characters are used to tell the phone to switch to another alphabet version e.g. Turkish, Urdu or Tamil.

8-bit data: 140 characters

Messages encoded with this character set are pretty rare. It's similar to the GSM-7 character set, but it has more characters which perform special functions rather than being displayed. If you've received messages which change the settings of your phone they're likely to have been sent with the 8-bit data alphabet.

16-bit UCS-2: 70 characters

The USC-2 character set is the most comprehensive. It includes support for a wide variety of alphabets including Cyrillic, Arabic, Chinese, Korean and Japanese. However, having so many characters to choose from means that the code for each character must be longer. This is the reason why UCS-2 has a significantly lower maximum number of characters than the others.

Based on the characters you use, your phone will automatically select the alphabet with the highest maximum number of characters.

Who Set the Limits

German communications researcher Friedhelm Hillebrand, was the guy who originally came up with the 160 character limit.

In 1985 Hildebrand was the chairman of the Nonvoice Services Committee of the Global System for Mobile Communications (the organisation responsible for developing the standards for mobile communication). His goal was to balance being able to communicate complex messages with keeping bandwidth requirements as low. After sitting at a typewriter writing messages to himself, he found that 160 characters was enough to send relatively complex short messages.

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Comments

author avatar Sivaramakrishnan A
10th Dec 2012 (#)

Interesting share - siva

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