Why is the SMS only 160 characters long?

SMS messages allow people to send short text messages between mobile devices. In the English alphabet, these messages are limited to 160 characters including spaces. This limitation is based on the system within which SMS messages work. Instead of the traditional telephone communication, SMS messages use channels to send small packets of information between mobile phones and cell towers. The 160 character limit is actually such a consequence of the modest use for which this channel was established. The channel was chosen as the base channel for SMS, for the reason that it can be easily implemented with the elimination of the need for new infrastructure. 

Mobile phones are supported by a network of towers that are responsible for call transmission. These towers constantly communicate with the mobile devices they support using a frequency called the control channel. This control channel is used to relay information about the location of the phones and towers. It is also used to control calls. Unlike these calls, the SMS processes really require little exchange of information. When the providers decided to just transmit these short text messages, this channel was easy to use. 

The system was designed by the GSM (Global System for Mobile Communications) organisation. This organization studied the types of messages that people send to each other and concluded that users find this communication useful, even if they only transmit between 100 and 200 characters. The hardware was limited to a limit of 1120 bits within which a small number of characters of 7 bits each could be encoded. This yielded a maximum baud rate of 160 characters (1120/7 = 160 characters). 

Various other factors can reduce the character limit. Users can send longer SMS messages by concatenating groups of packets. However, this limit is reduced to 153 because each must contain metadata that describes the relationship to other components of the longer SMS message. Users who wish to communicate via other alphabets are also limited in the number of characters. Chinese, Arabic and Cyrillic messages use UTF-16 encoding. This requires 16 bits per character. Sending multiple messages just using UTF-16 reduces the number of characters in an SMS message to 67 characters. 

The limit of 160 characters per SMS message has also become common knowledge for various organizations. We can give an example here for one of the very popular services, namely Twitter. Messaging through this platform is also limited and allows posts of a maximum of 140 characters.