The character limit for one SMS is 160 characters. It is possible to send multiple SMS together, formed as a single, longer SMS; this is called a Concatenated SMS:
a one-part message will allow you to send up to 160 characters - you are charged for 1 message.
a two-part message will allow you to send up to 306 characters - you are charged for 2 messages.
a three-part message will allow you to send up to 459 characters - you are charged for 3 messages.
and so on.
To join messages together to ensure they deliver as one, a 7-byte concatenation header is used at the beginning of each SMS. Since this header is within the message, it reduces the total size of each SMS to 153 characters each.
Please also be aware that if you are sending in Unicode, your character count per SMS lowers to 70 characters for a one-part message due to the fact that each UCS2 character requires 2 bytes. The 7-byte header for concatenated messages will also apply sending in excess of one message. As a result, a two-part Unicode message has a limit of 134 characters and a three-part Unicode message has a limit of 201 characters.
Take a look at the Sinch SMS Product page to learn about Sinch's SMS products, or click here to sign up to our self-service portal and get started and send your first message today!