Multipart & Unicode SMS Messages

Learn more on how multipart and unicode SMS Messages

Andrew Craig avatar
Written by Andrew Craig
Updated over a week ago

Normally, a single SMS message can contain up to 160 characters. Longer SMS messages are split into multiple parts and reassembled by the recipient's handset.

Chattabox can send multipart SMS messages (also known as concatenated SMS or long SMS) up to 2,000 characters, although we recommend minimizing the number of SMS parts in each message you send. Your mobile network or SMS provider will charge you separately for each SMS part (and may have their own maximum length that may be less than Chatti's limit).

When composing a message in Chattabox "New Message" dialog, Chattabox displays the number of parts in your message:

However, the maximum length of a single SMS part actually depends on which characters are contained within the message:

Depending on the characters you use in your SMS message, the actual maximum number of characters in a single SMS part may be only 70 characters instead of 160 characters .

The maximum length of 1 SMS part depends on whether any characters in your message are not in the GSM 7-bit default alphabet . The default alphabet contains most characters on a "qwerty" keyboard as well as some common accented characters from European languages. If your message contains characters not in this alphabet, such as characters from non-Latin based scripts, then the message will be encoded as Unicode (UTF-16), in which case
the maximum number of characters per SMS part will only be 70.

Even if your message contains only one character that's not in the GSM default alphabet, the entire message will need to be formatted as Unicode -- even if it has multiple parts.

Additionally, the maximum size of each part in a multi-part SMS is slightly lower than 160 or 70 characters, because each multi-part SMS needs to contain a few bytes of additional data to tell the handset how to reassemble the message.

If the message only uses GSM 7-bit characters, then 160 characters will fit in 1 SMS part, and 153*n characters will fit in n SMS parts for n>1.

If the message contains other characters, then only 70 characters will fit in 1 SMS part, and 67*n characters will fit in n SMS parts for n>1.

When sending a message from Chattabox, our platform will prompt you to confirm if the message needs to be split into a multi-part SMS, since they are more expensive to send than a single part SMS.

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