Multi-part SMS

A standard SMS is limited to 160 characters, but you can use the system to send up to three messages joined together in a multi-part SMS. This article will discuss the mechanics behind multi-part SMSes, how you can send them, and how we bill for them.

Character Count

Brevity is key when you are sending SMSes, and every character counts. A standard SMS has a 160 character limit, but sometimes you need more space to get your message across properly. Multi-part SMSes allow you to send up to three joined messages. Each SMS, after the first, must have an identifying string of characters (which is not visible in the message), to keep the message together. The system automatically inserts these headers, which take up seven characters per SMS.

Number of SMSes Header Length Maximum Length
1 - 160
2 14 306
3 21 459


Personalisation Fields

Multi-part SMSes support personalisation fields. You can use these fields to instruct the system to insert personal details for each SMS recipient (such as their name, email address, etc.). If a personalisation field is long enough so that your message will need to be sent as a multi-part SMS, the system will automatically create the second message. Personalisation fields are counted as having zero characters while you are drafting the message.

When the system is sending messages, and adding the personal information, it automatically calculates how many messages are required. If you have selected the automatic opt-out link, the system will remove enough characters from your message for this link to appear in full. Make sure you leave space for this link, it takes 23 characters if you are writing in English.


Your contacts can reply to any of the individual messages in a multi-part SMS, and the system will identify who it came from and which message the reply was sent in response to. This applies to messages that require a subscriber response, and opt-out messages.


The system sends SMSes until your account runs out of SMS credits, it will then pause the unsent messages until the account is topped up. If this happens, you will need to resume the message sending manually.

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