SMS character counter.

The subtleties of SMS message length

SMS messages are measured in chunks of characters called parts, which is fundamental to understanding how they work. Every telephone operator in the world uses this concept to charge for messages sent. The total length of a text message affects not only the number of parts it will contain, but also its overall cost.

SMS length constraints are important to consider when optimising sending costs. For example, an SMS message is limited to 160 characters with GSM-7 encoding, and 70 characters with UCS-2 encoding. However, most current phones and networks allow messages to be segmented, concatenated and reconstructed up to 1600 characters. When the character limit is exceeded, the message is split into several parts, requiring specific management to reconstitute it correctly at the recipient's end. This process involves adding a user data header to each part to tell the phone how to reconstruct the original message. As a result, each part of the message contains only 153 characters using the GSM-7 encoding or 67 characters using the UCS-2 encoding for long concatenated SMS messages. Once all the parts have been received, the phone assembles them to display them as a single SMS to the end user.