SMS Length

Modified on Thu, 14 Sep 2023 at 12:12 PM

As the name implies, SMS stands for Short Message Service, indicating that these are short text messages. However, the length of SMS messages that can be sent from Click & Sign is not always the same, and it depends on two factors:

  • Text Encoding 
  • Types of SMS 


Text Encoding

Text encoding refers to the process of translating letters input by users into codes that are interpreted by operating systems of devices. 


The encoding commonly used for sending SMS is known as GSM encoding, defined by the GSM Association, a global association of mobile network operators. GSM encoding is based on ISO-8859-15, also known as latin-1. 


This encoding includes all alphabetic characters, both uppercase and lowercase, along with various diacritics, umlauts, special characters like ç or ñ, and a wide array of symbols. 


When characters from different alphabets or symbols not covered by GSM encoding, such as €, are used, the text is encoded using Unicode. 


The primary difference arises from the fact that Unicode encoding consumes twice the storage capacity in comparison to GSM encoding, leading to a reduction in the length of the text message. 

Based on the encoding, the length of an SMS can be: 

  • GSM Encoding: 160 characters per single SMS. 
  • Unicode Encoding: 70 characters per single SMS.


If an SMS message exceeds this length, it can be concatenated up to 5 messages, but it's important to note that the resulting length after concatenation is not an exact sum, as some internet data space is lost during concatenation.


For example, when concatenating 2 SMS messages, based on the encoding, you get the following lengths: 

  • GSM: 306 characters for two concatenated SMS messages. 
  • Unicode: 134 characters for two concatenated SMS messages. 


It's also important to consider that each mobile network operator has its own text re-encoding algorithms to try to provide maximum fidelity to the original message, so the same SMS may appear slightly different depending on the recipient's operator. 

We advise refraining from including currency symbols like € or $ in SMS messages and suggest employing the ISO 4217 currency code associated with the respective currency, such as EUR, USD, GBP, COP, PEN, etc. 

Types of SMS

Click & Sign provides a variety of SMS message categories, encompassing the initiation of the signature process, the sending of one-time codes, and the delivery of notifications. Here's a breakdown of the types and their maximum lengths: 


  • First step of the signing process: 2 concatenated SMS messages, accommodating 306 characters in GSM encoding and 134 characters in Unicode encoding.
  • Reminders:  2 concatenated SMS messages, accommodating 306 characters in GSM encoding and 134 characters in Unicode encoding. 
  • All other types: 1 SMS message in GSM encoding and 2 concatenated SMS messages in Unicode. 

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